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Plant Diversity
Ethnobotany Forestry Horticulture Photosynthesis and Respiration Plant Biotechnology Plant Cells and Tissues Plant Development Plant Diversity Plant Ecology Plant Genetics Plant Nutrition
Phil Gibson and terri r. Hopkins Series Editor . Gibson Professor Emeritus of Biology university of Western ontario William G.Plant Diversity J.
associations. II. Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. some addresses and links may have changed since publication and may no longer be valid. without permission in writing from the publisher.Plant Diversity Copyright 2007 by Infobase Publishing All rights reserved. or by any information storage or retrieval systems. You can find Chelsea House on the World Wide Web at http://www. Gibson. QK46.chelseahouse. III.D58G53 2006 580—dc22 2006023234 Chelsea House books are available at special discounts when purchased in bulk quantities for businesses. 0-7910-8960-6 (hardcover) 1. p. electronic or mechanical. J. Terri R. cm. Series. All links and Web addresses were checked and verified to be correct at the time of publication. Phil Gibson and Terri R. — (The green world) Includes bibliographical references and index. Plant diversity—Juvenile literature. recording. Gibson. Phil. Because of the dynamic nature of the Web. or sales promotions.com Text and cover design by Keith Trego and Ben Peterson Printed in the United States of America Bang IP 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper. I. For information contact: Chelsea House An imprint of Infobase Publishing 132 West 31st Street New York NY 10001 ISBN 10: 0-7910-8960-6 ISBN 13: 978-0-7910-8960-6 Library of Congress Cataloging-in-Publication Data Gibson. . No part of this book may be reproduced or utilized in any form or by any means. including photocopying. Title. Plant diversity / J. institutions.5.
Introduction vii 2 18 32 1 2 3 4 The Diversity of Plant Life The History of Plant Systematics Fungi and Algae Seedless Nonvascular Plants The Bryophytes 50 62 5 Seedless Vascular Plants 6 Nonflowering Seed Plants The Gymnosperms The Angiosperms Glossary Bibliography Further Reading Index 78 7 Flowering Plants 94 112 123 125 129 .
World exploration and discovery was driven by the search for herbs and spices. Gardening is one of the fastest growing hobbies in North America and the production of ornamental plants contributes billions of dollars annually to the economy. Psychologists tell us that plants also provide a sense of well-being and peace of mind. wood for building our houses. and other events of passage. funerals. Indeed we should thank green plants for providing the food we eat. fiber for the clothing we wear. and the oxygen we breathe. humans and other animals simply could not exist. Without plants. Ever since. which is why we preserve forested parks in our cities. Hopkins "Have you thanked a green plant today?" reads a popular bumper sticker. and install plants and flowers in our homes and workplaces. The cultivation of New World crops—sugar. vii . Human history has been strongly influenced by plants.By William G. The rise of agriculture in the Fertile Crescent of Mesopotamia brought previously scattered hunter-gatherers together into villages. the availability of land and water for cultivating plants has been a major factor in determining the location of human settlements. Gifts of flowers are the most popular way to acknowledge weddings. surround our homes with gardens.
Yet today. The Green World series opens doors to the world of plants. exploding population growth. and tobacco—was responsible for the introduction of slavery to America. what plants do.viii introduction cotton. Plants are so much a part of our environment and the fabric of our everyday lives that they rarely register in our conscious thought. mostly to North America. More often than not the question would be met with a blank. and where plants fit into the overall scheme of things. urban sprawl. As a young university instructor directing biology tutorials in a classroom that looked out over a wooded area. I would ask each group of students to look out the window and tell me what they saw. The push westward by English colonists into the rich lands of the Ohio River valley in the mid-1700s was driven by the need to increase corn production and was a factor in precipitating the French and Indian War. faced with disappearing rain forests. the productive capacity of global agricultural and forestry ecosystems is put under increasing pressure. . the human and social consequences of which are still with us. and concerns about climate change. The Irish potato famine in 1847 set in motion a wave of migration. The series describes what plants are. Plant Diversity introduces us to the seemingly endless variety in plant life. Understanding plants is even more essential as we attempt to build a sustainable environment for the future. We also learn the significance of plant diversity in planetary ecosystems and why understanding and protecting this diversity is critical to our own health and survival. that would reduce the population of Ireland by half over the next 50 years. from the smallest alga to the tallest trees. questioning look.
The Diversity of Plant Life 2 .
It is my pleasure here to take Botany as my special study. 1753 . today however the abundance of material for choice has made it the most extensive of all the sciences. —Carolus Linnaeus (1707–1778) from the preface of Species Plantarum. which previously was the knowledge of a few plants.
and scents (Figure 1. For the earliest hunter-gatherers. complete their life cycle in a matter of weeks. tools. The VaLue oF PLanT DIVeRsITy Knowledge and appreciation of plant diversity has always played a vital role in human survival. Individuals who knew which plants to use. and even cacao (Theobroma cacao).1). early humans learned not only which plants to eat. They thrive in the jungles of the Amazon basin. the plant from which chocolate is made. fruit. Plants make up a significant portion of the diet of the more than 6 billion people on this planet. Plants provide lumber and other construction materials for housing. coming in all different colors. Carelessly eating the wrong kind of leaf. where to find them. it was essential to know which plants were edible and which were not. They provide fibers for 4 . were used in religious ceremonies. As cultures developed. Plants such as sacred lotus (Nelumbo nucifera). They survive in the sands of the Sahara. and dyes. The plants themselves are no less diverse than their surroundings. but also which plants provided materials for housing. such as bristlecone pine (Pinus longaeva). can live hundreds or even thousands of years. or healers whose skill could mean the difference between life and death for their people. Humans also learned which plants had medicinal properties. such as annual bluegrass (Poa annua) and pool sprite (Amphianthus pusillus). whereas individuals of other species. medicine men. or seed could cause sickness or even death. clothing. They live in the cracks of New York City sidewalks. sizes. shapes. they also give clues to the evolutionary history of plants and insights into the history of life on Earth. peyote (Lophophora williamsii). Some plants. people still depend on plants for their survival. and how to prepare them were held in high regard as shamans.The Diversity of Plant Life Plants can be found nearly everywhere on Earth. Today. These diverse features not only indicate the ability of plants to adapt to their environment.
the diversity of Plant Life 5 a b c d Figure 1. and a bouquet of pink tulips (d). ferns found in the Bialowieza Forest in Poland (b). a cholla cactus (c). .1 Plants display a wide variety of forms. Photographed above are pine cones in a cluster (a).
6 Plant diversity clothing and other items. . Through photosynthesis. In the past. Even the modern pharmaceutical industry continues to depend on plants. Ethnobotanists are scientists who study the ways in which indigenous peoples use plants. particularly for medicinal purposes. continue to have a negative impact on plant diversity worldwide. anthropologists. plant diversity is also important to the functioning of planetary ecological systems. Thus. and biochemists are currently working with native peoples around the world to learn about medicinal uses of different plants to preserve cultural traditions and knowledge. such as humans and other animals. particularly habitat destruction. influence precipitation patterns. In addition to being useful to humans. with more than 25% of prescription drugs containing compounds extracted from plants. Plants regulate temperature. appreciating and understanding plant diversity is critical for the survival and quality of all life on Earth. can use. many human activities. Unfortunately. Ethnobotany Researchers estimate that more than 80% of the world's population still depends directly on plants for herbal medicines. Plants direct the cycling of nutrients between the soil and other living organisms. and perform many other essential ecological processes. ethnobotanists. provide habitat for other organisms. plants convert energy from the sun into other forms of energy that nonphotosynthetic organisms. many medicines have been developed from plants used for healing purposes by tribal peoples. Development of effective conservation strategies to protect botanical resources will depend greatly upon knowledge of plant diversity and its ecological importance. Many botanists. Billions of dollars are spent annually on ornamental plants and flowers.
For example. A plant may have more than one common name. and crabapple are examples of common names frequently used by scientists and nonscientists alike. and phylogeny. Common names are often easy to remember and are familiar to the general population. poison ivy. Common names sometimes suggest a plant's uses (broom straw. Common names often describe some aspect of a plant's physical appearance. In the 1700s. is a common name that identifies several different tropical tree species that produce small avocados. Aquacatillo ("little avocado"). Common names are given to plants by the people who live near them. and rattlesnake master are colorful. The names henbit. However. wax goldenweed and Spanish gold both refer to the same plant species. Grindelia ciliata. but give little information about the plant itself. Scientists currently use this binomial nomenclature . this is not always the case. for example. It is made up of three subdisciplines: taxonomy. loblolly pine. dogwood. scouring rush) or warn of its dangers (stinging nettle. classification. common names can be a problem for scientists because they are not necessarily specific to a single plant. Names like pitcher plant. A plant often has two names: a common name and a scientific name. fish on a line. Consequently.the diversity of Plant Life 7 The sTuDy oF BIoLoGIcaL anD BoTanIcaL DIVeRsITy The branch of biology that studies biodiversity is known as systematics. there are no rules to govern their application. and they provide limited information about a plant or its characteristics. cat's claw. cottonwood. A common name may refer to several plants with similar characteristics. or leafy elephant foot conjure images familiar to everyone. match weed. death camas). Sunflower. a Swedish botanist named Carolus Linnaeus (1701–1778) reduced the polynomial (many name) system to a binomial system. Taxonomy is the process of naming individual plants or groups of plants.
which is considered the starting point for modern taxonomy). 4. A name is valid if it has been published in scientific literature and contains a complete description of the plant written in Latin. For example. but they are two different species. 5. . A valid name for a species consists of two parts. 2. A plant or group of plants can have only one valid name. For example. or any associations with a particular culture. regardless of the language they themselves speak. but species names are never used alone. Latin was chosen because this was the language of the classical works of botany and other sciences. The first part of the name (Vitis) is the genus and the second part (vinifera) is the species. 3. The valid name for a species is the one first published closest to the date May 1. These two parts may not be the same. Carya glabra (pignut hickory) and Rhus glabra (smooth sumac) have the same species name glabra (meaning "without hairs"). the scientific name for the European grape is Vitis vinifera. All names are in Latin or have been Latinized regardless of a plant's location. A genus name can be used only once. The following are some of the fundamental ICBN rules: 1. a genus name and a species name. but a particular species name can be used in combination with different genera. A genus name can be used alone to refer to all members of a genus. Scientists around the world can communicate with certainty about a specific plant. The genus and species names are italicized or underlined.8 Plant diversity (two name) system of scientific or Latin names to identify species. 1753 (the publication date for Carolus Linnaeus' book Species Plantarum. 6. The use of scientific names for plants is based upon a set of rules called the International Code of Botanical Nomenclature (ICBN). its possible uses.
Botanists from around the world meet every Families With two names Although the ICBN states that there can be only one correct name for any group.the diversity of Plant Life 9 7. but have been in use for so many years (centuries. The botanical rules of nomenclature are independent of the rules that govern naming of other organisms. The older names deviate from ICBN rules.1 ICBN name Plant Families With Two Valid Scientific Names Older name Common name Apiaceae Arecaceae Asteraceae Brassicaceae Clusiaceae Fabaceae Lamiaceae Poaceae Umbelliferae Palmae Compositae Cruciferae Guttiferae Leguminosae Labiatae Gramineae Parsley family Palm family Sunflower family Mustard family Garcinia family Bean family Mint family Grass family . accepted names. in some instances) that many botanists still use them today. Table 1. The modern names have endings consistent with the ICBN rules. There are many other rules in the ICBN that give order to the process of naming. there is an exception to this rule. Eight plant families have two correct.
A species is a particular kind of organism that typically can reproduce with other members of the same Table 1. like a series of nesting boxes.2 International Code of Botanical Nomenclature Endings ICBN ending Scientific name Taxonomic Level Kingdom Division Class Subclass Order Family Genus Species Common Name -ae -phyta -opsida -idae -ales -aceae Plantae Embryophyta Angiospermopsida Asteridae Asterales Asteraceae Grindelia Grindelia lanceolata narrowleaf gumweed . is the process of grouping named organisms into an ordered system. and make sure that the ICBN is serving the needs of the botanical community. most inclusive grouping is the kingdom (all plants are in the Kingdom Plantae).10 Plant diversity five years at the International Botanical Congress to discuss rules. the smallest. Smaller groups are placed together into progressively larger groups. The second part of systematics. propose changes. In modern classification systems. classification. and least inclusive of which is the species. the largest. Plants are then divided into successively smaller groups.
Members of the same species all share an evolutionary history distinct from that of other species. which are abbreviations for the word species (sp. Through this system.2). Orders. For example. Animalia. all plant family names end with the suffix -aceae. most biologists recognize six kingdoms: Bacteria. systematists can show how organisms evolved. the classification level above family. refers to a single species and spp. end in -ales. how different organisms are evolutionarily related to one another.. Archaea. and how different groups have diverged and differentiated from one another throughout time. One of the most commonly used words is taxon (pl. botanists can quickly recognize the taxonomic level of any name. Through this type of research. which are branching diagrams that show the evolutionary family tree for a group. or spp. the evolutionary relationship among organisms. The final component of systematics is the study of phylogeny. Protista. The ICBN dictates specific endings for names at the different levels of plant classification (Table 1. Fungi. species and can be distinguished from other species based on a number of different characteristics. Studies of phylogeny often result in the construction of dendrograms. sIx KInGDoms oF LIFe Although there are differences of opinion. taxa). which refers to a group at any classification level. and . refers to multiple species).the diversity of Plant Life 11 taxonomic Abbreviations Systematists have developed their own terms and shorthand abbreviations to refer to different taxonomic groupings. Genus names can be used alone or followed by the abbreviations sp.
eukaryotic organisms that are heterotrophs. The remaining four kingdoms are eukaryotic. as well as their modes of obtaining nutrients and energy. Animals ingest the organisms they feed upon and secrete enzymes that break down their food into simple molecules. . however. This group includes the true bacteria and cyanobacteria (blue-green algae). Kingdom Protista contains organisms that share similarities with animals. meaning that their cells lack a nucleus and membrane-bound organelles within them. Kingdoms Eubacteria and Archaea contain descendants of the oldest organisms on Earth. Kingdoms Animalia and Fungi contain multicellular. Cellular and molecular data. Kingdom Bacteria is very diverse and contains a majority of the prokaryotic organisms on Earth. have shown conclusively that fungi are not plants and should be placed in a separate kingdom. and plants. genetic data have shown that fungi are actually more closely related to animals than to plants. In contrast. such as hot springs and deep sea thermal vents. meaning that their cells contain a nucleus and membrane-bound organelles. they must consume other organisms to obtain the nutrition and energy they need to live. Members of these two kingdoms are prokaryotic. Kingdom Protista contains many unicellular organisms and simple multicellular organisms. and then absorb the digested food from the environment. Organisms are placed into one of these kingdoms based upon their genetic and cellular features.12 Plant diversity Plantae. Interestingly. Of particular importance are the green algae. which played an important role in the evolution of plants. Fungi were long considered plants. Kingdom Archaea is another diverse group. in conditions similar to those found in Earth's early history. fungi. fungi secrete enzymes onto their food source. which are absorbed by tissues of the digestive system. Many members of this kingdom often live in harsh environments.
there may be as many as 500. Several unique features. however. that do not produce photosynthetic pigments and are not photosynthetic. make it possible to group these organisms into their own kingdom. such as dwarf mistletoes (Arceuthobium) and Indian pipe (Monotropa uniflora). Plants also reproduce and interact with other living things. that they can then use to meet their own needs and provide energy to other living things. use energy and nutrients in their metabolism. Plants conduct photosynthesis using unique combinations of different pigments.2). such as cellulose or lignin. such as sugars and starch. Plant cells are surrounded by a wall made of complex carbohydrates. but only plants and green algae contain the other photosynthetic pigments. The plant cell wall is another unique feature of these organisms. and have evolved a variety of adaptations that help them survive in their environment. such as chlorophyll a. They conduct the biochemical process of photosynthesis in structures called chloroplasts (Figure 1. A vast majority of plants are photoautotrophs. despite this. WhaT Is a PLanT? Like all living things. and carotenoids. Plants are divided into four major groups: bryophytes. plants are composed of cells. . chlorophyll b. Through photosynthesis. their biology and other traits clearly indicate that they are plants.the diversity of Plant Life 13 Kingdom Plantae contains organisms that are autotrophs. plants convert energy in sunlight into chemical forms of energy. gymnosperms. Some photosynthetic bacteria contain chlorophyll b. which means that they are capable of producing their own energy.000 different plant species on Earth. seedless vascular plants. It is worth noting that there are parasitic plants. which provides rigidity and structural support for the plant body.000 different species of plants. and angiosperms. Botanists have identified more than 300.
the plant egg is not capable of movement and thus remains in female gametophyte tissues.14 Plant diversity Figure 1. which protects the developing gametes. and chloroplasts. Another defining trait of plants is that the structures in which gametes (eggs and sperm) are produced are surrounded by a layer of cells called the sterile jacket. Furthermore.2 Plant cells are made out of many components. . cell wall. including a nucleus.
the diversity of Plant Life 15 The aLTeRnaTIon oF GeneRaTIons All living things have a life cycle. The spores germinate to form the gametophyte. Mitosis is a similar process. The most familiar life cycle to most people is that of animals. The sporophyte is a plant that produces spores. This unique type of life cycle is called the alternation of generations because during sexual reproduction there is an alternation between a multicellular haploid generation called the gametophyte and a multicellular diploid generation called the sporophyte (Figure 1. Eventually. it produces two identical cells with the same amount of genetic material as the original parent cell. Gametes are haploid (contain one complete set of chromosomes). The sporophyte grows through mitosis. but instead of halving the genetic material in the cell. special cells in its reproductive tissues (spore mother cells) undergo meiosis to form haploid spores. dominates the life cycle. and the cycle repeats itself. Zygotes and adults are diploid (contain two complete sets of chromosomes). The alternation of generations is important in the study of plant diversity because the four major groups of plants differ with regard to which generation.3). . Through fertilization. the gametophyte is the dominant generation. dividing twice to produce four haploid cells. Haploid cells are produced when diploid cells undergo the process of meiosis. whereas the sporophyte is the dominant generation in angiosperms. gametophyte or sporophyte. in which single-celled gametes unite during sexual reproduction to form a multicellular zygote that grows and develops into a mature adult. Plants go through haploid and diploid phases in the life cycle. The gametophyte is a plant that produces gametes. for example. the egg and sperm unite to form a zygote that becomes the diploid sporophyte. In bryophytes.
summaRy Plants are an important component of life on Earth. . Plants also provide a multitude of natural resources for humans and have performed important roles in the evolution of humans and the growth of human cultures and populations. The result of fertilization is the formation of a zygote. Sporophytes undergo meiosis to form spores. combine during fertilization. Gametophytes have half the number of chromosomes as sporophytes.16 Plant diversity Figure 1.3 Plants alternate between sporophyte and gametophyte phases. or gametes. which initiates the gametophyte phase. Male and female gametophytes. They provide a variety of ecological services ranging from the production of food through photosynthesis to providing habitats for other living things.
but also to understand its origins and evolutionary history. .the diversity of Plant Life 17 Through systematics. botanists identify and organize the diversity of plant life not only to catalogue botanical diversity.
The history of Plant systematics 18 .
The botanist is he who can affix similar names to similar vegetables. so as to be intelligible to every one —Carolus Linnaeus . and different names to different ones.
Ancient texts and records describing medicinal.300 years ago. botany—like other sciences—lay mostly dormant until the Renaissance. which ushered in the so-called Age of Herbals. One of the oldest such books was written more than 4. This book was one of the primary medical references in Europe until the 1600s. For the first time. this classic work of Eastern medicine went through 12 editions and was even translated and published in Japan in 1625. or shrub). The renewed interest at this time coincided with the invention of the printing press. fruit. organizing them into groups based on characteristics such as their growth form (herb.500 years ago by Emperor Chi'en Nung of China. Roman naturalist Pliny the Elder (a. The ReBIRTh oF BoTany In Europe. it was also the first botany book to include illustrations.d. wrote De Materia Medica (The Material of Medicine). leading German 20 . 40–90). tree. First published in 1108. Dioscorides (circa a. the Greek naturalist Theophrastus wrote about the cultivation and uses of various plants. He eventually established the first known botanical garden. a Chinese physician named Tang Shen-wei published Cheng Lei Pen Ts'ao (The Materials of Medicine Arranged According to Pattern). agricultural. Not only did De Materia Medica contain written descriptions. a book that classified and described more than 600 plants. and leaves.d. an unknown author wrote the Ebers papyrus. He gathered much of the information for his book Historia Plantarum (History of Plants) by studying the gardens of Athens. More than 2. and other uses of plants have survived from cultures around the world. One thousand years later. a Greek physician in Nero's army.20 The history of Plant systematics Plant diversity The earliest efforts to categorize plants were based on their usefulness to humans. 23–79) described the horticultural and medicinal uses of many plants in his book Historia Naturalis (Natural History). One thousand years after Pliny and Dioscorides. a scroll that described the pharmacological uses of plants found in ancient Egypt.
Hieronymus Bock. were able to publish and widely distribute books that had descriptions and pictures of plants (Figure 2.1). This illustration of a peony is from an herbal published in 1613.the History of Plant Systematics 21 Figure 2. invented the process of . and Leonart Fuchs. working at the University of Pisa. such as Otto Brunfels.1 Herbals are books that describe the many characteristics of plants used in herbal medicines. The first universities in Upper Italy and Europe established botanical gardens to study live plants. botanists. Luca Ghini (1490–1556).
collecting. as well. genera. however. Their discoveries led to the development of the first classification systems based on features of the plants rather than their uses. such as John Ray (1628–1705) and Pierre Magnol (1638–1715). Many professional systematists work at herbaria associated with botanical gardens. dried whole plants or parts of plants are mounted on pieces of paper called herbarium sheets. Although researchers continued to focus on the medicinal uses of plants. In the herbarium. . described and named numerous European and Asian species. caRoLus LInnaeus By the eighteenth century. This led to a polynomial system that was cumbersome and impractical. a library of preserved plant materials. Naturalists. Each sheet has a label that identifies the plant and tells where and when the specimen was collected and by whom. Specimens collected by Linnaeus are in herbarium collections around the world. for that matter.22 Plant diversity What is an Herbarium? An herbarium is a library of pressed and dried plants. There was no standardized system or consensus. the full name for one plant species was Serratula foliis ovato-oblingis accuminatus serratis. about how to name a plant—or any other kind of organism. For example. stored. and classified a great deal of plant material from around the world. and drying plants to create the first herbarium. pressing. colleges. These botanists and others began to clarify concepts about plant families and genera that would become the foundation of modern systematics. botanists of the seventeenth century began to investigate other areas. The herbarium established in 1532 by Ghini's student Gherhards Cibo (1512–1597) is the oldest still in existence. and families. studied. or universities. botanists had collected.
such as Michel Adanson (1727– 1806) and Antoine Laurent de Jussieu (1748–1836). fruits. Several paintings show Linnaeus wearing or holding a small cluster of Linnaea flowers. naTuRaL cLassIFIcaTIon sysTems anD eVoLuTIon Although his binomial system was successful. This arbitrary approach produced an artificial classification system. whose work developed the concept of plant families. preferred to use a multitude of different features (for example. Although he was not the first person to consider a simplified binomial system. The genus Dioscorea (yams) is named in honor of the Greek botanist Dioscorides.2). Linnaeus gave binomial names to more than 7. Linnaeus categorized plants based on the number and arrangement of stamens. De Jussieu described more than 100 plant families. The genus Magnolia is named after the botanist Pierre Magnol. Linnaeus's classification system was not widely accepted. and then subdivided them using other floral traits. Using this approach. When the binomial system (see Chapter 1) was introduced by Carolus Linnaeus. In Species Plantarum. and leaves) to group plants based on overall similarity. Famous Botanists remembered Scientists often recognize individuals who have made major contributions to the field of botany by naming plants after them. calcybus subrotundis. flowers. a genus that was named after him.300 species (Figure 2.the History of Plant Systematics 23 floribus corymbosis. this was shortened to Serratula glauca. many of which that are still recognized today. Linnaeus was the first to develop and consistently use a workable naming system—one that has been in use for more than 200 years. published May 1. Contemporaries of Linnaeus. which grouped unrelated species together. 1753. .
. Linnaea borealis.24 Plant diversity Figure 2. This famous picture of Linnaeus in Lapland dress shows him holding a cluster of flowers named after him.2 Carolus Linnaeus is known for his contributions to modern taxonomy.
or genealogy. Natural selection occurs when organisms have traits that help them survive better or produce more offspring than those that lack those traits. Prominent botanists. • Plants with woody stems are more primitive than herbaceous plants. organisms with adaptive traits leave more descendants. and Karl Prantl (1849–1893) in Germany. Charles Darwin described how species evolve and how adaptations and other traits spread through the process of natural selection. and Asa Gray (1810–1888) and Charles Bessey (1845–1915) in the United States. Adolf Engler (1844–1930). . such as A. many stamens or carpels) are less advanced than flowers with fewer parts. August Wilhelm Eichler (1839–1887). George Bentham (1800– 1884) and Sir Joseph Hooker (1817–1911) in England. P. This approach produced a natural classification system that reflected evolutionary relationships among plants. eVoLuTIon-BaseD cLassIFIcaTIons As the theory of evolution spread. The goal of producing natural classifications was further enhanced with the publication of The Origin of Species in 1859. developed classification systems in which they considered the evolutionary history of specific traits.the History of Plant Systematics 25 De Jussieu was one of the first botanists to group related species and families together. In this groundbreaking book. With his theory of evolution. and the adaptation becomes more prevalent in future generations. Darwin showed that the diversity of life could be interpreted as a family tree. Through greater survival and offspring production. de Candolle (1778–1873) in Sweden. that reveals how taxa have changed throughout time. botanists quickly developed evolution-based classifications. Some general rules they followed in developing evolution-based classifications included: • Flowers with many parts (for example.
Ledyard Stebbins (1906–2000). the theory of evolution is not a guess. . and Rolf Dahlgren (1932–1987) of Denmark produced major classification systems for angiosperms that influenced modern thinking on flowering plant evolution. Researchers continue to develop classifications that display the evolution of different plant groups. Thus. moDeRn cLassIFIcaTIons Arthur Cronquist (1919–1992). Scientists use the term theory to refer to a collection of unifying principles that explain proven facts and observations. cLaDIsTIcs anD consTRucTInG PhyLoGenIes Systematists construct phylogenies using an approach called cladistics. and Robert Thorne (b.26 Plant diversity • Species with flowers containing male and female structures are less advanced than species with flowers that contain only male or only female parts. These groups seek to clarify our understanding of the history of life on Earth by investigating large-scale patterns of plant evolution. klados. such as the Angiosperm Phylogeny Group and the Tree of Life Project. but a well-supported scientific explanation for the diversity of life. 1920) of the United States. a term that comes from the Greek word for branch. systematists working in many different laboratories and herbaria take part in international collaborative efforts. the Meaning of theory Evolution is sometimes discredited as a theory and not a fact. This new evolutionary perspective gave rise to modern classifications that show the phylogeny or evolutionary history and relationships among organisms in a lineage. Armen Takhtajan (b. Currently. 1910) of the former Soviet Union.
For a cladistic study. systematists first determine which characteristics are primitive (ancestral) and then which are advanced.1 Comparison of Traits Between Algae and Major Green Plant Groups Seedless vascular plants yes Trait Presence of chlorophylls a and b Sterile jacket layer around antheridia and archegonia Vascular tissue Seeds Flowers Algae yes Bryophytes yes Gymnosperms yes Angiosperms yes no yes yes yes yes no no no no no no yes no no yes yes no yes yes yes The objective of cladistics is to produce a natural classification in which every descendant of a single ancestor is placed on the same branch (clade) of a dendrogram. The presence of a particular trait is a more evolutionarily advanced condition than the absence of a trait.1 shows five different traits in the four major groups of plants and algae. For example. Table 2. it is called a monophyletic group. By identifying monophyletic groups. plants without vascular tissue . For example. systematists can determine how specific traits in a lineage evolved throughout time. When all of the descendents of a common ancestor are placed in the same clade.the History of Plant Systematics 27 Table 2.
3 The above cladogram shows the relationship among major plant groups. the absence of vascular tissue in a group of plants is a more primitive condition than the presence of vascular tissue. Therefore. The data in Table 2. Cladists use the patterns of how advanced traits arise to determine evolutionary relationships among members of a lineage.3) that describes the phylogeny for the major groups . (xylem and phloem) appear in the fossil record before plants with vascular tissue.28 Plant diversity Figure 2.1 can be used to produce a cladogram (Figure 2.
which help users identify plants by leading them through a series of paired questions. systematists do not collect any form of data that one could specifically identify as systematics data. In the early stages of systematics. In some ways. These books often have pictures and descriptions that make it easy for budding botanists to learn the common plants of an area. gymnosperms.the History of Plant Systematics 29 Botanical resources There are many resources available for individuals who want to explore the botanical diversity around them. and ultimately the angiosperms. cycles. Instead. fruit type. or the ecologist who collects data on the size and distribution of populations. they use the techniques of other scientific fields to collect data that they can then use to develop a classification. More advanced students may require a flora. With the invention of the microscope. that is correct. the geneticist who collects data on the sequence of genes on a chromosome. which typically contains an extensive listing of species that occur in an area. and processes in cells. Unlike the physiologist who collects data on the metabolic rates. This cladogram shows that all plants shared a distant common ancestor with algae. Field guides and floras typically contain dichotomous keys. . The DaTa sysTemaTIsTs use Systematics has been referred to as the field of science with no data of its own. botanists depended heavily on morphology (the outward structural appearance of a plant). Traits such as leaf shape. Bryophytes are the oldest plant lineage. of plants. Systematists use the branching patterns of a cladogram to develop their classifications. or number of parts in a flower are easy to observe and compare among living and fossil plants. botanists turned to anatomy (the internal cellular structure of a plant) to develop classifications. followed by the seedless vascular plants. One good resource is a field guide.
A (adenine). . Each band represents a single fragment of DNA known as a nucleotide. There are four types of nucleotides. abbreviated G (guanine).30 Plant diversity Figure 2.4 DNA sequencing gels are used by modern-day taxonomists to collect genetic data. T (thymine). and C (cytosine).
Throughout time. Early artificial classifications were based primarily upon a plant's usefulness to humans. there were tremendous advances in the ability to extract and sequence DNA from plants and improved computing ability to analyze data from DNA (Figure 2. and interpreting the history of plant diversity. summaRy Throughout human history.the History of Plant Systematics 31 The field of systematics is constantly changing as different technological advances arise. it does illustrate how botanists continue to think about naming. such as family or order. classifying. but many different individuals have contributed and continue to play a significant part in this field of study. systematists proposed moving away from the Linnaean system toward a system called the Phylocode. In the 1990s. it only recognizes clades. Linnaeus is one of the best-known names in the history of botany. . Although there is skepticism about the value of such a system and how it would affect the study of plant diversity overall. Instead. which has no hierarchical rankings. New techniques combine new data with earlier forms of data to further refine the understanding of plant evolution. systematists developed natural classifications that present the evolutionary history of plant groups. systematists began to collect chemical data for their studies. As instruments and techniques for analysis of plant chemical extracts improved in the 1940s. Systematists rapidly incorporated these new techniques into their analyses. There is even continued discussion among plant systematists about how organisms should be named and classified.4). individuals have worked to describe and organize the diversity of plant life on Earth. Recently.
Fungi and algae
Did you hear about the fungus and the alga? They took a lichen to each other.
Fungi and algae
Although there are many beneficial species of fungi, people often
fear them because of their toxins and other undesirable features. For example, fungi called molds cause allergies and other respiratory illnesses. Other species produce strong hallucinogenic compounds that have a range of effects on the nervous system. Other fungi, however, produce chemicals that benefit humans. The important antibiotic penicillin is derived from the fungus Penicillium chrysogenum. As a further example, the yeast Saccharomyces cerevisiae is an invaluable fungus used to make bread, beer, and wine. Like so many of the fungi, algae too are often overlooked or unwanted. A thick growth of algae can pollute ponds and render water undrinkable (Figure 3.1). Fish tanks often need to be cleaned to remove algal growth. Other algae, however, are valued for their usefulness. Nori and sea lettuce are used in Asian cooking. Carrageenan, a product derived from algae, is used in ice cream, sauces, shampoos, cosmetics, air fresheners, and many other products. Algae are also of immeasurable ecological importance in oceans, lakes, and streams, where they are the foundation of the food chain. At different times, fungi and algae have been classified as plants. Although these groups do share similarities with plants, fungi differ enough to warrant their own kingdom. Whether algae should be placed in a different kingdom, however, depends on which alga is being considered. Fungi and algae have played vital roles in plant evolution. An ancestral algal species established itself in the terrestrial environment and gave rise to all plants. This invasion of land was made possible through interactions between plants and fungi. Because early plants had no roots, plants and fungi formed relationships in which fungi provided plants nutrients from the soil. A majority of plants today still form these important symbiotic relationships with fungi.
Fungi cell walls. Like plants. FunGI Mycology (from the Greek word for fungus. and other related animals). crustaceans. are composed predominantly of chitin (a substance also found in the external skeletons and shells of insects.Fungi and Algae 35 Figure 3. Fungi are composed of many small threadlike strands of cells called hyphae. The collection of hyphae that make the fungal . fungi are multicellular eukaryotes whose cells produce a cell wall. however. mykes) is the study of fungi.1 Excessive growth of algae can reduce the quality of freshwater lakes and ponds.
The honey mushroom (Armillaria ostoyae) is a fungus that attacks the roots of conifers. haploid mycelia of different mating types come into contact with one another.4 square miles) and may be more than 2. their nuclei can remain separate within them and grow as a mycelium composed of these dikaryotic cells." the fungi kingdom also has individuals of tremendous size and age. spores are formed in a specialized structure called a sporangium (plural: sporangia) and then released to the environment. The mycelium of one individual in southwest Washington State was measured to cover 1.36 Plant diversity the Humongous Fungus While several plants are candidates for the title of "largest or oldest organism on Earth. allowing cells from different hyphae to fuse. Fungi are heterotrophs that feed on living and dead organisms. organic molecules. extremely important as decomposers that clear organic waste from the environment and return nutrients to the soil. sexual reproduction occurs between genetically different mating types. Fungi range in size from unicellular yeasts to the immensely large individuals that cover great areas in forests. Another. which are then absorbed.400 years old. along with bacteria. This method of feeding makes fungi. covers 2. Fungi do not have male and female individuals. Instead. In asexual reproduction. BasIc FunGaL LIFe cycLe Many fungi reproduce asexually as well as sexually. They obtain energy and nutrients by growing hyphae through the body of their food source and secreting enzymes that break it down into smaller.500 acres (approximately 2. Although the cells combine. simpler.5 square miles).200 acres (3. Whether the separate nuclei fuse . growing in eastern Oregon. For sexual reproduction. body is called a mycelium.
For example.100 157 32.1 Group Major Groups of Fungi Common name Estimated species Chytridomycota Zygomycota Glomeromycota Ascomycota Basidiomycota chytrids zygomycetes arbuscular mycorrhizal fungi sac fungi club fungi 1.2) and have estimated that the total number may be close to 1. mycologists recognize five major phyla (equivalent to the botanical level of division) of fungi: chytrids (Chytridomycota).000 . but their classification has been challenging.Fungi and Algae 37 immediately to form a zygote or continue to grow as a dikaryotic mycelium until forming a zygote at a later time is a distinguishing feature among different types of fungi. majoR FunGaL GRouPs Mycologists have identified and named more than 50. which had long been classified as fungi.1 and Figure 3. recent advances in the collection and analysis of genetic and other molecular data have allowed mycologists to determine that the water molds (Oomycota) and slime molds (Dictyosteliomycota and Myxomycota).000 species of fungi (Table 3. zygomycetes (Zygomycota).000 1. arbuscular mycorrhizal Table 3.00 26. Presently.5 million. but are in fact protists. Fungi are a monophyletic group. are not fungi at all.
a bunch of mushrooms at the base of a withered plum tree (c). and the fungal pathogen Candida albicans.2 Fungi display a wide range of growth forms. In the above photographs. two fly agaric mushrooms (a). as seen under a microscope (d).38 Plant diversity a b c d Figure 3. cultured Beauveria bassiana (b). .
club fungi. club fungi (Basidiomycota). and sac fungi (Ascomycota).3).3 groups. Arbuscular mycorrhizal fungi. and sac fungi are more advanced groups. This cladogram shows the phylogeny of major fungal .Fungi and Algae 39 fungi (Glomeromycota). Figure 3. Current perspectives on fungal evolution indicate that the chytrids and zygomycetes are the oldest lineages (Figure 3. Club fungi and sac fungi are closely related and encompass 95% of all known fungi.
fungi first evolved in the seas.40 Plant diversity Chytrids Chytridomycota are the oldest group of fungi.100 species. In asexual reproduction. fused hyphae from different mating types form a zygospore (the small black dots seen in moldy bread). Cells undergo meiosis in the sporangium and release the haploid spores. highlights this group's . arbuscular mycorrhizal fungi. A frequently encountered zygomycete is the common bread mold in the genus Rhizopus. They live primarily in or near water and are the only group of fungi to produce spores and gametes with flagella (singular flagellum). Arbuscular Mycorrhizal Fungi Mycologists recently moved a group out of Zygomycota and classified them as a new phylum. Zygomycetes Zygomycota are a relatively small fungal group of about 1. Glomeromycota. Chytrids are important decomposers of plant material in many aquatic systems. like all other organisms. A chytrid called Batrachochytrium dendrobatidis is currently attacking amphibian populations worldwide and may be responsible for the extinction of several amphibian species. During sexual reproduction. A zygospore is highly resilient to environmental conditions and can remain dormant until environmental conditions cue favorable conditions for releasing spores. Their common name. The chytrid life cycle is simple. Haploid spores germinate and form a haploid mycelium. a tail-like structure that gives cells the ability to move. The gametes fuse and immediately form a diploid mycelium that eventually forms a sporangium. sporangia form on the tips of upright hyphae and release numerous spores. The presence of flagella in this lineage provides evidence that. which releases male and female gametes.
a small group of chestnuts was discovered near Warm Springs.Fungi and Algae 41 important features. Asci form on the edge of a large reproductive structure called an ascocarp that is characteristic of these fungi. a disease known as chestnut blight was accidentally introduced into North America from China or Japan. This type of plant-fungus mutualism occurs in the majority of plants on Earth. the fungus provides the plant with nutrients from the soil. different mating strains chestnut Blight American chestnut (Castanea dentata) once accounted for 25% of the trees in the eastern forests of North America. During sexual reproduction. Arbuscular mycorrhizal fungi are obligate mutualists. mean- ing that they are unable to live without their plant host. In return. in the early 1900s. Mycol ogists cannot even culture them in the laboratory. Sac Fungi Ascomycota is a large group that includes more than half of all known fungi. Arbuscules are specialized structures formed by the fungus inside the plant cell that enable the plant and fungus to exchange nutrients. The disease. In April 2006. however. Then. The arbuscular mycorrhizal fungi are the only group of mycorrhizal fungi that form these specialized structures. Their common name (sac fungi) comes from the sac-shaped structure called an ascus (plural: asci) that forms during sexual reproduction. attacked native chestnut trees and by 1940 had driven the species to the brink of extinction. Sexual reproduction has never been observed in any member of this group. caused by the fungus Cryphonectria parasitica. . Mycorrhizae (which literally means "fungal root") are fungi that grow on a host plant's roots. Scientists believe that these trees survived because the site is too dry for the fungus. The plant provides the fungus with a carbohydrate energy source. Georgia.
oyster mushroom (Pleurotus ostreatus). The gills on the undersurface of the basidiocarp form numerous basidia in which the dikaryotic nuclei fuse to form a zygote. The genus Penicillium includes the source of penicillin (Penicillium chrysogenum). Ascomycetes are important decomposers in many ecosystems. There are also many beneficial ascomycetes. and shiitake mushroom (Lentinula edodes) are eaten on salads. and then immediately undergo meiosis to form haploid spores. The white button or portabella mushroom (Agaricus bisporus). The single-celled zygote then undergoes meiosis to form haploid spores that are released to germinate and produce new mycelia. Amanita bisporigera. toadstools. the nuclei fuse. The mycelium then forms an ascocarp with the asci on it. formed during sexual reproduction. The zygote is the only diploid cell in the entire basidiomycete life cycle. the sexual reproduction of basidiomycetes begins with the joining of dissimilar mating strains. The sac fungi also include many species that cause disease in a wide variety of crops and wild species. which germinate to establish a new mycelium. and Amanita verna are known as death angel fungi because of . pizzas.42 Plant diversity fuse. Club Fungi The mushrooms. and puffballs common to forests and front yards are members of the Basidiomycota. forming a dikaryotic mycelium. As in other groups of fungi. and many other dishes. called a basidium (plural: basidia). The resulting dikaryotic mycelium forms a reproductive structure called a basidiocarp (the familiar mushroom). and the yeast used in brewing and baking (Saccharomyces cerevisiae). Morels (Morchella) and truffles (Tuber) are considered delicacies by some individuals. Amanita virosa. the blue cheeses (Penicillium roqueforti and Penicillium camembertii). Inside the asci. The name club fungi refers to the club-shaped sporangium. Club fungi are a diverse group that has many different properties and uses.
attacks many cereal crops. their lethal toxins and almost pure white color. a fungus that causes plant disease. Shelf fungi are important decomposers of wood and other plant materials.4 Smut. Above. Fly agaric (Amanita muscaria) and psilocybin mushrooms (Psilocybe cubensis) produce hallucinogenic compounds that have been used by shamans—a religious specialist or medicine man—in ancient cultures and religions worldwide. .4). Club fungi called rusts and smuts are serious plant pathogens that cause billions of dollars in crop damage annually (Figure 3.Fungi and Algae 43 Figure 3. mature smut galls are exposed on an ear of corn.
their origins can be traced back more than 900 million years. some of the haploid cells release flagellated.44 Plant diversity aLGae Phycology. Throughout the course of time. This diversity has allowed algae to succeed in a wide range of habitats. . covers a wide range of photosynthetic organisms—from minute diatoms. During sexual reproduction in multicellular species. asexual reproduction via spore formation or cell division is common. The resulting diploid zygospore undergoes meiosis and releases haploid unicellular individuals. to the enormous kelps that grow in the cold oceans of northern latitudes. Green alga Life cycle Green algal life cycles include sexual and asexual reproduction. because of their importance and familiarity to humans. more complex. Cells are also typically haploid in multicellular green algae. Others perform the same ecological role in freshwater ecosystems. the study of algae. Some even grow in snow. Some green algae have even evolved unusual associations with other organisms. Two other groups—the red algae (division Rhodophyta) and the brown algae (family Phaeophyceae)—are also included here. Green Algae Green algae are ancient. multicellular growth forms. In unicellular algae. sand. where they form the base of marine food webs. Sexual reproduction in unicellular green alga involves flagellated. Algae live in soil. as well as larger. Many live in the oceans. haploid individuals of different mating types simply coming together and fusing nuclei. however. Green algae are of particular importance because they are the group from which land plants evolved. whose shells display intricate patterns and structural variations. the one original unicellular species diversified to form other unicellular species. and on the barks of trees.
thus. Prasinophytes are important because they make up some of the oldest lineages of green algae and are therefore representative of the first green algae to evolve. and on land. They exhibit a number of different growth forms ranging from singlecelled species (Chlamydomonas). and the delicate. fresh water. One such relationship involves the sloth. chlorophytes. however. where sloths usually dwell. This group includes several separate lineages and. although some live in brackish water (a combination of . and the charophytes. sheet-like sea lettuces (Ulva). This coloration helps camouflage the sloth. The resulting single-celled zygote undergoes meiosis and releases haploid spores that grow to become multicellular individuals.000 species. In return. The sloth gets its greenish hue from the algae that live in its fur. spheroid colonies (such as Volvox).Fungi and Algae 45 it's not Easy Being Green Algae are well known for their mutualistic relationships with fungi.500 species of green algae that live in salt water. Chlorophytes are a group of approximately 7. unicellular gametes. which join in a process similar to that of unicellular algae. the algae get a place to live and exposure to the light that is present high in the forest canopy. Charophytes are predominantly freshwater or terrestrial algae. is not a monophyletic group. protecting it from predators. There are three major groups within the green algae: prasinophytes. Less well known. filamentous forms (like the genus Oedogonium). Green algae Lineages are Related to Land Plants Green algae are a large group with more than 17. a mammal that lives in the canopy of tropical forests. Prasinophytes are a diverse group of unicellular marine algae. are their mutualistic relationships with animals.
Species in these groups also retain the zygote in the gametophyte tissues. The genus Spirogyra contains many filamentous species commonly encountered in freshwater lakes and ponds. Charophytes. . such as flagellated sperm and nonmotile eggs. Species in the genera Chara and Choleochaete also have reproductive traits.46 Plant diversity salt and fresh water). These groups differ from plants in several ways. Charophytes are the only organisms other than plants that produce pigments called flavonoids. like chlorophytes. a trait that has helped preserve evidence of them in the fossil record. include a diversity of unicellular and multicellular growth forms. Systematists believe that algae in the Chara lineage are the living descendents of a common ancestor shared by green algae and land plants. there is continuing discussion about whether plants and green algae should be grouped together or separately. but they also differ in important ways. Some charophytes in the order Charales are called stoneworts because of calcium deposits in their cell walls. but they lack the sterile jacket cells found in plants. and because they are photosynthetic autotrophs. Red Algae (Rhodophyta) and Brown Algae (Phaeophyceae) The debate about the exact relationship between green algae and modern plants does not extend to the red and brown algae. that are similar to terrestrial plants. Because they share structural features with the green algae. Relationship Between Green algae and Plants Green algae share a number of traits with plants. In addition. Algae lack a sterile jacket layer around their gamete-producing structures. whereas the female gamete is retained on the maternal individual in plants. Although systematists agree that land plants evolved from a green alga ancestor. a vast majority of algae release their gametes into the water. however. they are included in this discussion of groups that are related to land plants.
but a few basidiomycetes also form lichens. which is an air-filled structure that holds the kelp upright.000 marine species.5). many unicellular algae live embedded in a fungus (Figure 3. The algae provide carbohydrates and other nutrients to the fungus. These pigments are particularly good at absorbing what little light there is in the deepwater environments where many red algae species live. Often. LIchens Lichens are interesting organisms that develop from a mutualism between fungi and algae or cyanobacteria. the cells of red algae are covered by a jellylike substance (mucilage) or contain deposits of a certain type of mineral (calcium carbonate). they do not cause the red tides that kill fish and other marine life. More than 98% of the fungi that form lichens are ascomycetes. Although some red algae produce toxic substances. Red tides are actually caused by population explosions of protists known as dinoflagellates. Lichens exist in extremely stressful environments. brown algae differ from plants in the photosynthetic pigments they contain. They get their characteristic color from the high amount of reddish pigments called phycobilins in their cells. The deepest known photosynthetic organism is a red alga that has been found living 268 meters below the water's surface. Blades often have a float.500 species that live mostly along the rocky shores of cold ocean waters. a stipe (or stem). In lichens. in which neither the fungus . Among other things. Red algae are a large group of approximately 6. these materials help the red algae survive in deep water. most of which are multicellular. such as tree branches or bare rock. Kelp is an important brown alga that forms extensive underwater "forests.Fungi and Algae 47 Brown algae are a small group of approximately 1. and blades (leaves)." The kelp body has three specialized regions: a holdfast that anchors the kelp. which in turn provides a livable environment for the algae.
The above image is of Lobaria pulmonaria. photographed in Oregon. nor algae could live alone.5 Lichens are symbiotic organisms with algae embedded in a fungal matrix. . the most widespread Lobaria lichen.48 Plant diversity Figure 3. This ability to survive in harsh environments allows lichens to be among the first colonizers of bare rock surfaces.
Environmental scientists therefore use lichens as indicators of air pollution. Symbiotic relationships with mycorrhizal fungi allowed early plants to colonize the land. . bright conditions of bare rock. Fruticose lichens range in appearance from the multibranched individuals of reindeer moss (Cladonia subtenuis) to the erect pillars of British soldier (Cladonia cristatella). and continue to help them still. Their ecological function as decomposers makes nutrients in the soil available to plants. lichens are quite sensitive to air pollution. heterotrophic organisms.Fungi and Algae 49 Lichens display three different growth forms. Despite their ability to tolerate the hot. dry. fungi and algae are important in any discussion of plant diversity and evolution. summaRy Although they are not plants. Foliose lichens have a leafy appearance. Green algae are a diverse group of unicellular and multicellular photosynthetic organisms whose characteristics indicate that all terrestrial plants evolved from a single algal ancestor. Fungi are multicellular. Crustose lichens are flat. they often appear to be painted on the surfaces where they grow.
seedless nonvascular Plants The Bryophytes 50 .
. took thousands of years for its growth. the peat of the valley of the Somme is a formation which. . in all likelihood. —Charles Lyell (1797–1875) British geologist . .
seedless nonvascular Plants The Bryophytes More than 500 million years ago. for example. hornworts (Anthocerotophyta) and true mosses (Bryophyta). a multicellular species of alga became the first organism to make the transition from living in the water to living on land. In response to these new environmental conditions. FeaTuRes oF BRyoPhyTes Bryophytes are typically small plants. air does not provide the structural support or the nutrients that water does. There are between 20. Although often overlooked because of their diminutive size. Because of this. they produce no vascular tissue or seeds. Living in shallow waters. Their size is limited because they lack vascular tissue. The plants were probably thin.000 and 25.000 species of bryophytes (Table 4. the study of bryophytes can provide insight into some of the first strategies evolved by plants in their adaptation to life on land. Traits evolved in this species that allowed it not only to tolerate the dry periods at low tide. Instead of 52 .1) classified into three divisions: liverworts (Hepatophyta). early plants began producing a cuticle—a thickened layer of waxy material on the outer surface of cells that prevented them from drying out. which provides the structural support and nutrient transport necessary for larger growth. Plants adapting to land had to overcome certain challenges. but also to survive farther from the edge of the water. Kingdom Plantae was born. Bryophytes are nonvascular plants.1) are the living descendents of these earliest plants. allowing nutrients to enter and spread throughout the plant body (vascular tissue for specialized transport would not evolve for another 50 to 100 million years). and the botanical invasion of land had begun. ranging from a few millimeters to several centimeters in height. From these simple beginnings. this ancestor of all plants experienced alternately wet and dry conditions with the rise and fall of the tides. These modern bryophytes have retained many features of their ancestors. bryophytes (Figure 4.
1 Bryophytes are small. . green moss (a type of bryophyte) covers three oak tree trunks. nonvascular plants. Above.Seedless nonvascular Plants 53 Figure 4.
archegonia (egg-producing structures). The structure and appearance of gametophytes and sporophytes differ among bryophyte groups.000 12.54 Plant diversity Table 4. a vast majority of bryophytes live in moist environments (Figure 4.2). Although some bryophytes can survive in very dry habitats. rhizoids do not have any greater water uptake ability than the rest of the plant. multicellular gametophytes called protonemas. threadlike.000–9. BRyoPhyTe LIFe cycLe The life cycle of bryophytes has distinct gametophyte and sporophyte generations. Bryophytes are restricted to moist environments partly because they lack vascular tissue. Haploid spores germinate into small. but also because water is required for sperm to swim to the eggs during sexual reproduction.000 using roots to take up water and anchor themselves in place (as plants do). These protonemas mature and produce gametophytes with antheridia (sperm-producing structures). Most bryophytes produce antheridia and archegonia on the same . The short-lived sporophyte is attached to and nutritionally dependent upon the gametophyte.000–15. The free-living gametophyte is the dominant phase. Most bryophytes use their entire bodies to gather water and nutrients from the environment. bryophytes use specialized cells called rhizoids.1 Group Major Groups of Bryophytes Common name Estimated species Anthocerotophyta Hepatophyta Bryophyta hornworts liverworts true mosses 100–150 6. or both. Unlike root cells.
moss is present on a boulder near Silverton. . Colorado.2 Mosses are common in moist. In this photograph.Seedless nonvascular Plants 55 Figure 4. streamside habitats.
majoR GRouPs oF BRyoPhyTes Bryophytes are a relatively small group of plants containing approximately 24. and the major groups differ primarily in their reproductive structures.3 Marchantia is a typical liverwort. . It is a primitive plant related to mosses and ferns. the combined egg and sperm form a diploid embryo that will become the sporophyte. but mosses produce antheridia and archegonia on separate male and female gametophytes. The young sporophyte is attached to the gametophyte and will remain attached to the gametophyte for its entire life. All bryophytes are structurally simple plants. Sperm cells use whiplike flagella to propel them down a narrow canal toward the egg. Spore mother cells inside the sporangium will undergo meiosis to form the haploid spores that will start the cycle over again. After fertilization. Because the sperm must swim to the egg. A sporangium forms at the tip of the sporophyte. male and female gametophytes must grow near one another.56 Plant diversity gametophyte. Figure 4.000 species.
The basic body form of a liverwort consists of a simple. flattened thallus with pronounced structural differences between their upper and lower layers. that has a very simple branching pattern (Figure 4. The lobed liverwort thallus was used to treat liver complaints because it resembles a human liver. The remainder of the liverworts are in a clade called the complex thallus liverworts. . The suffix -wort comes from the Old English word wyrt. These plants have a broader. moist areas near streams and waterfalls.3). The genus Marchantia contains species common to cool. The males produce antheridia on raised flattened structures which. flattened. These plants are in a clade called the leafy or simple thallus liverworts. This comes from a belief known as the Doctrine of Signatures. Marchantia may also reproduce vegetatively by fragmentation of parts from a larger. meaning "herb. Liverworts Liverworts are the second largest bryophyte division." The Doctrine of Signatures was a popular medical concept through the nineteenth century and is still used by some practitioners of homeopathic medicine.000 species.000– 9. older plant body. with 6. when hit with a drop of water. rounded structure attached to the underside of the female gametophyte. Marchantia produces separate male and female gametophytes. Early physicians and herbalists thought a plant that resembled an organ could be used to treat ailments of that organ. launch the sperm from the gametophye. The sporophyte is a small. allowing the parent plant to reproduce asexually through vegetative reproduction. Females produce archegonia on a raised structure that has a drooping appearance. shady. These masses of vegetative cells can splash out of the cups.Seedless nonvascular Plants 57 doctrine of Signatures Liverworts and an assortment of other plants include the names of various organs in their common names. Gemmae (singular: gemma) are small masses of tissue that may form in cuplike structures on the thallus. leaflike thallus.
4 Hornworts are most commonly found in damp. Oregon.4). they produce antheridia and archegonia on the upper surface of a thallus. The production of stomata may be an important evolutionary link between hornworts and plants that evolved later. humid. Hornworts Hornworts are the smallest bryophyte division. Like the liverworts.000 species. however. mosses. Mosses The most familiar of the bryophytes. with 12 genera and only 100–150 species.000–15. undisturbed locations. They grow in a wide range of conditions ranging from moist areas along streams and in forests to arctic and alpine environments. Hornworts are seen here in Lincoln County. Hornworts resemble vascular plants in that their sporophyte is photosynthetic and produces stomata (openings that allow water and gasses to be exchanged between the plant and the atmosphere). the sporophyte grows from the upper surface of the thallus and has an elongated horn or spindle shape (Figure 4. with 12. are a very successful group. In hornworts. Mosses are typically divided into .58 Plant diversity Figure 4.
The name moss. . Many mosses have a leafy appearance with areas of photosynthetic tissue that resemble leaves. however. Club moss and spike moss are seedless vascular plants related to ferns. Reindeer moss is not a plant at all. Granite mosses are an even smaller group of approximately 100 species. however. and true mosses (Bryopsida). is applied to various plants and nonplants outside of this group. Sphagnum peat bogs cover approximately 1% of the Earth's surface. they are not true leaves.Seedless nonvascular Plants 59 three classes: peat mosses (Sphagnopsida). The true mosses are the most common. granite mosses (Andreaeopsida). When mature. Technically. The mature sporophyte is composed of a capsule on the tip of a long stalk called a seta. mosses produce specialized transport cells. but rather a lichen. hydroids and leptoids lack some of the defining features of true vascular tissue. moss gametophytes can dominate the landscape with extensive mats of vegetation. the capsule dries. The moss sporophyte grows from the top of the female gametophyte. releasing the numerous spores inside. Although individual plants are small. Nevertheless. A Moss By Any other name Confusion between common and scientific names is nowhere more evident than in the term moss. such features indicate a close relationship between mosses and vascular plants. Cells called leptoids transport sugars. Because these structures lack vascular tissue. Spanish moss and rose moss are angiosperms. and function to transport water up the moss stem. The peat mosses are a small group with two genera and more than 400 species. These blackish-green or reddish-brown mosses grow in clumps in mountains and granite outcrops. Cells called hydroids are found in the central stem of some moss species. Irish moss and the moss in ponds and lakes are actually algae. mosses are the plants in the group Bryophyta. Similar to vascular plants. Although they function like vascular tissue.
8 65 144 206 248 290 354 417 443 490 543 4550 Formation of Earth Forests of large. Bryophytes probably diverged from the lineage that gave rise to vascular plants about 430 million years ago.2). primitive trees Seedless vascular plants dominate. anD PhyLoGeny oF The BRyoPhyTes Spores and fragments of ancient bryophytes have been found in fossils that date back almost 445 million years (Table 4. DIVeRsIFIcaTIon.60 Plant diversity Table 4. Fossils of ancient liverworts have been found . These fossils and other data suggest that bryophytes evolved from their algal ancestor between 490 and 500 million years ago.2 Eras The Geological Timescale Periods Beginning (mya)* Major botanical events Cenozoic Mesozoic Paleozoic Quarternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian 1. first seed plants First vascular plants Plants invade land Conifers dominant Radiation of flowering plants Evolution of flowering plants Precambrian *mya: million years ago oRIGIns.
it was used to dress and pack wounds. Peat is also important in the horticulture industry where it is used to lighten and increase the water-holding capacity of soil. which is largely Sphagnum. New evidence indicates. common ancestor. They may colonize disturbed sites early. ecoLoGIcaL anD economIc ImPoRTance Ecologically. they still depend on water to transport sperm to egg during sexual reproduction. all bryophytes were thought to have descended from a single. have suggested that hornworts may actually be the most closely related to vascular plants. True to their aquatic origins. Economically. hornworts. They grow in extensive mats and colonies that can help stabilize soils near streams. Sphagnum moss has a variety of different uses. nonseedproducing plants. . In the past. however. Known collectively as bryophytes. that bryophytes are actually three distinct monophyletic lineages. The arrangement of the three lineages.Seedless nonvascular Plants 61 in rocks dating back 360 to 408 million years. is burned as fuel in some northern temperate areas. Traditionally. Mosses are important components of food chains in many arctic and alpine environments. establish. and mosses are nonvascular. however. these were the first plants to successfully invade. however. Some studies. and mosses the most recently evolved group of bryophytes. Peat. and persist on land. Bryophytes are the only plants with a dominant gametophyte stage and a smaller sporophyte stage. bryophytes are important plants. Until recently. is not completely certain. summaRy Liverworts. however. beginning the process of ecological succession in which the plants growing on a site changes over time. with liverworts the next oldest. and moss fossils have been identified from as far back as 290 to 360 million years ago. in homes and in larger-scale electricity production. systematists believed hornworts to be oldest. bryophytes are of some importance.
seedless Vascular Plants 62 .
—Carolus Linnaeus .Nature does not proceed by leaps and bounds.
1). The second clade. One genus of tree. is the monilophytes. which forced the water out of their tissues. whisk ferns (Psilotales). They and their relatives formed extensive forests. the intense pressure and heat of geologic forces converted the plants into coal. and quillworts (Isoetales). these plants evolved vascular tissue. Lepidodendron and many of the other plants that eventually became coal were members of a group called the seedless vascular plants. the lycophytes (division Lycopodiophyta).seedless Vascular Plants The coal that powered the Industrial Revolution in the eighteenth and nineteenth centuries is still an important fuel source today. Over time. and other materials efficiently and effectively around the plant body. Coal formation began more than 300 million years ago. and the true ferns (Filicales). layers of sediments accumulated on top of the plants. marattioid ferns (Marattiales). During the course of millions of years. The monilophytes shared a common ancestor with the lineage that eventually gave rise to seed plants. in particular. Trees and plants that fell into the water as they died did not decompose because the low oxygen content of the water prevented it. contributed a great deal of plant matter to the coal beds. ophioglossoid ferns (Ophioglossales). This clade contains horsetails (Equisetales). previously known as the ferns and fern allies. contains three orders: the club mosses (Lycopodiales). Unlike the bryophytes before them. At present. 64 . The trunks of Lepidodendron trees stood more than 130 feet (40 meters) tall and were more than 6 feet (2 meters) in diameter. This and other important traits made the next great breakthrough in plant evolution possible. The oldest clade. seedless vascular plants consist of approximately 14. spike mosses (Selaginellales). nutrients. Many different lineages of seedless vascular plants have become extinct since they first evolved. a network of xylem and phloem that transports water. water ferns (Salviniales and Marsileales). when shallow seas covered the Earth and a warm tropical climate promoted lush plant growth.000 species in two monophyletic clades (Table 5.
Networks of tracheids not only aid the passage of water. but also support the plant body. mosquito ferns true ferns 380–400 700–750 125 15–17 15–25 75–110 200–240 75 16 11. Eventu- .1 Group Major Groups of Seedless Vascular Plants Common name Estimated species Lycopodiales Selaginellales Isoetales Psilotales Equisitales Ohioglossales Marattiales Marsiliales Salviniales Filicales club mosses spike mosses quillworts whisk ferns horsetails ophioglossoid ferns marattoid ferns water clover water spangles. along with the gymnosperms and angiosperms. These plants. form a group called the tracheophytes or vascular plants.500–12. The most primitive type of water-conducting cells.000 FeaTuRes oF seeDLess VascuLaR PLanTs Seedless vascular plants were the first to evolve vascular tissue.Seedless Vascular Plants 65 Table 5. are found in the xylem of seedless vascular plants. This internal reinforcement of the stem allowed plants of the Carboniferous to reach greater heights than ever before. tracheids. These cells are rigid due to the presence of lignin in their cell walls.
when photosynthetic tissue filled in the spaces between the finest branches at the tips of the stems. Larger roots enabled plants to extract water and nutrients from the soil more effectively. Larger roots also provided a stronger anchor and better structural support to the larger stems that were evolving above ground. the sporophyte dominates the life cycle in seedless vascular plants. the first vascular plants evolved roots. came the evolution of leaves.1). While the sporophyte in bryophytes is small and completely dependant upon the gametophyte. flattened areas of photosynthetic tissue surrounding a network of veins. The dominant sporophyte also allowed the plants to produce far more offspring than bryophytes. The ferns in particular evolved large leaves called fronds that produce sporangia on their underside in many species (Figure 5. Leaves are thin. The life cycle of seedless vascular plants also diverged from that of their bryophyte ancestors. Plants were evolving new structures below ground as well. the gametophyte and the sporophyte in the seedless vascular plants can be a free-living plant. which led to the evolution of wood and even stronger stems and branches. With vascular tissue. Furthermore.66 Plant diversity ally. Vascular plant leaves and stems have a thick cuticle layer on their outer surface that prevents water loss. Vascular tissue and leaves helped plants survive in a terrestrial environment and allowed them to colonize drier areas on land. Leaves evolved from highly branched stems of early vascular plants. plants evolved the mechanisms to produce and accumulate xylem in the stem. and sporophyte promoted the success of the seedless vascular plants. . These changes in the vascular tissue. Leaves also became much more elaborate and structurally diverse in seedless vascular plants. unlike the brypophytes. leaves. Instead of the simple rhizoids that attach bryophytes to the ground.
but they . the antheridia release the sperm. seeDLess VascuLaR PLanT LIFe cycLe The life cycle of a typical fern serves as a good example of the alternation of generations in seedless vascular plants. Spores are released from sporangia on the undersurface of the leaves. After fertilization. producing gametophytes with antheridia and archegonia (mosses have separate male and female gametophytes. heart-shaped. Another significant change involving the spores occurred in the seedless vascular plants. At maturity. and when the walls of the sporangium dry out.1 Sporangia are found on the underside of fern fronds.Seedless Vascular Plants 67 Figure 5. The spores germinate to form an independent. Sporangia contain spores. In the bryophytes and earliest vascular plants. the spores catapult away from the plant. all spores produced by a plant are identical (homospory). photosynthetic gametophyte. the embryonic sporophyte grows from the gametophyte. which then withers and dies while the sporophyte becomes the plant we know as a fern. which swim to and fertilize the egg housed in the archegonium.
200 species.000 species. hence the common name "ground pine" given to some club mosses. The plant spreads by a rhizome and has rudimentary roots. 10 to 15 genera. Microspores. Club Mosses Club mosses (Lycopodiales) are a small group with 3 genera and approximately 380 to 400 species. and other adaptations to the environments where they live.2). The sporophyte is a lowgrowing terrestrial plant with simple branching stems (Figure 5. Some vascular plants evolved the ability to produce different spores (heterospory). All lycophytes have simple leaves (microphylls) that contain a single strand of vascular tissue. majoR GRouPs oF seeDLess VascuLaR PLanTs Seedless vascular plants include a diverse array of more than 25. make the female gametophyte. spike mosses. The small. scalelike leaves bear a resemblance to those of many conifers. produced in a megasporangium. This was an important step toward the evolution of pollen and seeds that would occur later in the gymnosperms. Leaves are opposite one another on the stem.68 Plant diversity come from identical spores). Members of the major groups display a wide range of growth forms. produced in a microsporangium. which are often clustered at the ends of branches . Spores are produced in sporangia on specialized leaves called sporophylls. and quillworts. Megaspores. Lycophytes Lycophytes are a relatively small group of plants with 3 families. Lycophytes include the club mosses. life cycles. give rise to male gametophytes. Heterospory is a valuable trait because it allows some gametophytes to become specialized for sperm production and others for egg production. and approximately 1.
in Pennsylvania. Above. Club moss gametophytes are either photosynthetic or obtain nutrition from organic material in the soil through symbiosis with mycorrhizal fungi. These so-called resurrection plants become dormant when water is scarce. These leaves have a scalelike structure on their base. spike mosses produce leaves in four rows: two rows of small leaves above two rows of larger leaves. Spike Mosses The order Selaginellales has only 1 genus (Selaginella) and 700– 750 species. some live in dry environments. taking on a lifeless appearance.Seedless Vascular Plants 69 Figure 5. only to spring back to life when rehydrated.2 Lycopodium is a typical club moss. The sporophyte is a branching rhizome similar to that of club mosses. into a structure called a strobilus or cone. . Note the brown strobili at the ends of the branches. stiff clubmoss (Lycopodium annotinum) is found in the Pocono Mountains. Although most spike mosses live in the tropics. whereas the leaves of club mosses grow opposite one another.
Psilotales is a very small order. The genus Psilotum grows in tropical and subtropical areas. Plants have no roots. Psilotum has a simple body with small. There are six major groups within the monilophytes: horsetails. Monilophytes Monilophytes are a large diverse clade containing more than 12. water ferns. often being mistaken for clumps of grass—something that would never have happened to their lycophyte ancestors. marattioid ferns.70 Plant diversity Quillworts Isoetales is the smallest lycophyte order. quillworts are quite small. Why only small plants from the different seedless vascular plant lineages survived to the present is a mystery that botanists are still trying to solve. Recent analyses have shown that the small quillworts of today are the living descendents of the giant lycophyte trees that once dominated swamp forests more than 350 million years ago. ophioglossoid ferns. they spread by an underground rhizome covered with rhizoids. The sporophyte is a perennial corm that can be somewhat woody. grow from the top of the corm. Quillworts are relatively small aquatic plants that live underwater for part or all of their life.000 species. All monilophytes produce megaphylls. . most of which are capable of producing sporangia. whisk ferns. Tufts of long. Whisk Ferns Whisk ferns are absent from the fossil record. quill-like leaves. Both sporo- diminutive descendents of Giants Compared to other species of seedless vascular plants. with only 2 genera and 15–17 species. scalelike leaves and a stem that branches off into two smaller stems. leaves that have multiple strands of vascular tissue. with only a single genus (Isoetes) and 125 species. and true ferns.
with only 6 genera and about 200 species. They also produce upright stems. Their leaves are large. ancient horsetails known as calamites grew to tree size. The leaves of these ferns are divided into two distinct regions: one that is photosynthetic and sterile. The ridged stem is essentially a hollow tube of separate segments. Horsetails have a unique appearance. Horsetails Equisetales was once a diverse group. Although modern horsetails may reach heights of about 1 meter. produce upright stems. are a small group with 80–90 species. like Ophioglossoids. Branching rhizomes send up aerial stems. The horsetails are perennials that grow in moist areas and along waterways. are coiled into . Ophioglossoid Ferns Ophioglossales. Psilotum has distinctive sporangia that are borne in clusters of three on the stem. Marattoid Ferns Marattiales is also a small group.Seedless Vascular Plants 71 phytes and gametophytes form relationships with mycorrhiozal fungi. but it now contains only a single genus (Equisetum) with 15–25 species. whose silica deposits give them a rough texture. also called adder's tongue ferns. scaly leaves. unlike the sporangia of true ferns that develop from a single cell. Marattoid ferns. Young leaves of Ophioglossoid ferns are not coiled as in other groups. The sporangia of ophioglossoid ferns develop from a group of cells. which differ from the horizontal stems of true ferns. and when young. Oval sporangia at the tips of the stems produce the spores. At the joints of the segments there are rings of small. and another that is nonphotosynthetic and produces spores.
3 The fiddlehead is an identifying feature of marattoid and true ferns. These ferns were common in swamps and are well represented in the fossil record. Figure 5.72 Plant diversity a structure called a fiddlehead or crozier that uncoils as it opens (Figure 5.3). These ferns also produce a sporangium that develops from multiple cells. Above. . a fiddlehead is seen unraveling.
however. most common group of seedless vascular plants.Seedless Vascular Plants 73 Water Ferns Water ferns grow in freshwater ponds and lakes. Two water ferns. Despite this. and the other is feathery and hangs below the surface of the water. and their young fronds form fiddleheads. consequently. . This is particularly problematic because bracken fern fronds contain chemicals that are toxic to cattle that eat them. noxious weeds that can clog waterways and cause flooding. Ferns in Salviniales produce two types of fronds. with approximately 75 species in Marsileales and only 16 species in Salviniales. The floating fronds contain colonies of cyanobacteria that fix nitrogen for the fern and. Marsilea plants grow in shallow water or mud and produce fronds with long petioles and leaves that look like a four-leaf clover. There are two different orders of water ferns. True ferns are homosporous. As mentioned previously. Both are small groups. Marsileales and Salviniales. Salvinia molesta (kariba-weed) and Azolla pinnata (feathered mosquito fern) are aggressive. Their sporangia develop from single cells on the undersurface noxious Weedy Ferns Many ferns are attractive and desired plants. Their stems typically grow horizontally as rhizomes. True Ferns Filicales is the largest. one is flattened and floats on water. water ferns can be pests in some areas. Others. Bracken fern (Pteridium) can invade pastures and choke out native pasture plants. There are more than 11. true ferns have several features that separate them from other fern groups.000 species in 320 genera divided among 30–35 families. increase the nitrogen in the water where they grow. Both groups of water ferns encase their spores in a hard structure that can lie dormant in the mud for many years. are not.
small herbs. and even aquatic herbs. Tension generated by the annulus causes the mature sporangium to open and fling spores away from the parent plant. of fronds. spores are released from the sporangium.74 Plant diversity Figure 5.4 The annulus is a thickened area on the fern sporangium.4).5). True ferns grow in many temperate ecosystems. Above. Sporangia are clustered into structures called sori (singular: sorus) that are often covered by a flap of tissue called an indusium. including vines. Each sporangium has a thickened layer of cells called an annulus along one side of the sporangium (Figure 5. Large tree ferns grow in many tropical forests (Figure 5. but they are particularly common in tropical areas. Smaller ferns are common in the middle layers (known as . Ferns display a diversity of growth forms.
.5 Tree ferns are the largest living. The above image shows tree ferns in Malaysia.Seedless Vascular Plants 75 Figure 5. seedless vascular plants.
many species became extinct due to the drying of the environment that occurred during that time. but all three lineages were extinct by about 360 million years ago. During this time. and structural data. herbaceous lycophytes. Zosterophyllophyta. genetic. The split between the monilophyte clade and the seed plants occurred 20–30 million years later. Woody growth evolved approximately 380 million years ago. Seedless vascular plants can be divided into two distinct monophyletic clades (lycophytes and monilophytes) that are well supported by fossil. Production of wood evolved independently in several different lineages. these species only reproduce asexually. Living seedless vascular plants are of limited economic value beyond their usefulness in landscaping and as houseplants. oRIGIns anD ReLaTIonshIPs oF seeDLess VascuLaR PLanTs The oldest vascular plant fossils are of Cooksonia and date back approximately 410 million years (Table 4. These were small. Some fern species do not produce a sporophyte stage at all and exist only as gametophytes. leafless plants that spread by branching rhizomes.76 Plant diversity the understory) of forests worldwide. . They lacked roots. Thus. and appear to have used symbiotic relationships between their rhizoids and fungi to improve nutrient uptake from the soil. and Trimerophyta dominated the landscape 425 to 370 million years ago. simple. The split between the lycophyte clade and other vascular plants probably occurred more than 400 million years ago. Only the ferns. VaLue oF seeDLess VascuLaR PLanTs Seedless vascular plants are components of many terrestrial ecosystems. They spread by a central stem that grew along the ground and produced upright branches with sporangia at their tips.2). The early vascular plant lineages Rhinophyta. and horsetail lineages survived.
the lycophytes and the monilophytes. however. Initially quite small. seedless vascular plants diversified and evolved many massive species that were once the giants of the ancient swamps. summaRy Seedless vascular plants evolved more than 400 million years ago. there are two major lineages of seedless vascular plants. Presently. The evolution of vascular tissue enabled plants to become larger because of increased structural support and more efficient transport of materials around the plant body.Seedless Vascular Plants 77 Fiddleheads from some species are edible. and club moss spores were once used as an explosive in fireworks and in the development of photography. . are of immense value as an effective fuel source. Long-dead seedless vascular plants that became coal.
nonflowering seed Plants The Gymnosperms 78 .
The morning glory flower lives a single day.The pine tree lives a thousand years. Yet both fulfill their destiny. —Chinese proverb .
Harsh desert winds shred the leaves. bowl-shaped stem. or cones. which are torn into strips when the leaves are whipped by strong winds. one of the driest places on Earth.nonflowering seed Plants The Gymnosperms The Namib Desert. Unlike other members of the plant kingdom. The name gymnosperm comes from the Greek words gymnos (naked) and sperma (seed). An adult Welwitschia consists of two leaves. which may last as long as 2.1).1 The desert plant. The leaves and reproductive structures known as strobili. grow from the edge of the woody.000 years. is home to one of the strangest plants on Earth. Welwitschia mirabilis. 80 . The plants also collect water from cool fogs that blow in from the ocean. Welwitschia mirabilis survives by producing long taproots capable of accessing water from deep in the soil (Figure 6. Welwitschia produces only two leaves during its entire lifetime. Droplets of water that condense on the plant's leaves flow down them to water the soil around the plant. These seeds are considered Figure 6. is photographed in the Namib Desert in Namibia. Welwitschia belongs to a group of plants called the gymnosperms. The leaves emerge from the germinating seed as the plant grows. which continue to grow from their base.
2 Conifers are cone-bearing seed plants that display a variety of shapes and sizes. based on these naked seeds. Scottish botanist Robert Brown (1773–1858) was the first to classify gymnosperms as a group separate from the other seed plants. as angiosperm seeds are. Above. . to be naked because they are not covered by sporophyte fruit tissues. conifers surround a lake in northern Wisconsin.nonflowering Seed Plants 81 Figure 6.
The gymnosperm stem and roots have a meristem called . Some gymnosperms are grown commercially for different uses. but rather a modified stem axis called a cone scale. see Figure 6. Seeds also contain stored carbohydrates and nutrients that will feed the seedling as it begins to grow. cycads (Cycadophyta). higher latitudes and areas of high elevation.3). allowing them to evolve and diversify.82 Plant diversity There are approximately 840 species of gymnosperms represented by 4 divisions. Gymnosperms are vascular plants that produce xylem and phloem. ginkgos (Ginkgophyta). Seeds and pollen are produced in cones (Figure 6.2). Gymnosperms were the first plants to produce pollen as a way to carry sperm to the egg for fertilization. When the pollen grain germinates. a gymnosperm cone is a group of sporophylls attached to a short central axis. Unlike bryophytes and seedless vascular plants that release their sperm into the environment. FeaTuRes oF GymnosPeRms Seeds and pollen are two features that have enhanced the reproductive success of gymnosperms. to egg-containing ovules on female cones. typically by wind. Although sporophylls in most gymnosperms evolved as a modification of a leaf. Pollen is another critical trait to evolve in this group. and the sperm is released to fertilize the egg. Similar to the strobili in the seedless vascular plants. the female conifer cone (pine cone) is actually not a modified leaf. Some are restricted to warm tropical areas while others form extensive forests in colder. the conifers (Coniferophyta. the sperm cells of gymnosperms are encased in pollen grains that are transported. and gnetophytes (Gnetophyta). a pollen tube grows into the ovule. Seeds are an important evolutionary innovation because they protect the dormant plant embryos until environmental signals cue germination.
nonflowering Seed Plants 83 a b c d Figure 6. and a previous year seed cone beside clusters of male cones (d ). an eastern white pine cone (c). including a pine cone with open scales (a).3 An assortment of female pine cones are displayed above. a spruce pine cone (b). .
The mature pine tree is the adult sporophyte. A coast redwood (Sequoia sempervirens) in the Sierra Nevada Mountains of coastal California is the tallest tree on Earth. which also grows in California. and many of them achieve awe-inspiring size and age.500 years old. shedding their leaves once a year.700 years old. standing more than 365 feet (112 meters) tall and calculated to be more than 3. All gymnosperms are woody perennial plants. which produces wood-forming xylem and bark-forming phloem. such as larch (Larix) and bald cypress (Taxodium) are deciduous. (Sequoiadendron giganteum). At no point in the gymnosperm life cycle is there a free-living. These plants. whose seeds germinated before the pyramids of Ancient Egypt were built. however. A majority of them grow as trees or shrubs. GymnosPeRm LIFe cycLe The gymnosperm life cycle differs from those of bryophytes and ferns in its dramatic reduction of the gametophyte stage and increase in the sporophyte stage. are the oldest known living organisms. Each female cone is composed of numerous cone scales with female sporangia on them. a spore Gymnosperms of unusual Size and Age Some of the oldest and largest organisms on Earth are gymnosperms.84 Plant diversity the vascular cambium. The sporophyte is clearly the dominant phase. . retaining living leaves on the plant throughout the year.200 years old. is another tall gymnosperm species. A vast majority of gymnosperms are evergreen. In each female sporangium. The tallest sequoias are more than 276 feet (84 meters) tall and 3. independent gametophyte. The giant sequoia. A few. Female cones are produced on the ends of branches. Several bristlecone pines (Pinus longaeva) in the White Mountains of eastern California are more than 4. The life cycle of pines (Pinus) serves as a good example of a typical gymnosperm life cycle.
the cone scales open to release them. majoR GymnosPeRm GRouPs Gymnosperms are a relatively small group with approximately 800 living species (Table 6. The small opening in the integument is called the micropyle. Conifers With approximately 60 genera and more than 600 species.1). The female gametophyte and integuments form a structure called the ovule. papery male cones (Figure 6. The pollen grain makes contact with the female gametophyte. each containing an egg. In the small. and slowly grows a pollen tube into the female gametophyte tissue. Inside the ovule are multiple archegonia. Each spore develops into a pollen grain that contains a tube cell and a generative cell. the female cone matures. they are quite common and often maintain very large populations. Pollination occurs when the pollen grain is either blown directly into the micropyle or trapped on a droplet of water secreted from the micropyle and drawn into it. When the pollen tube reaches the archegonium (a process that can take up to a year). but only one survives. and the cycle begins again when the seed germinates to form a new seedling. Coniferophyta is the largest. germinates. Once the seeds are mature. Although there are few species. The embryo produced in the female gametophyte tissue begins to form a seed. As the seed develops during the course of another year. Pine and other gymnosperm pollen grains often form air sacs that help carry them on the wind to the female cones. forming the familiar woody pinecone. it releases the sperm cell to fertilize the egg. spore mother cells undergo mitosis to form spores.nonflowering Seed Plants 85 mother cell undergoes meiosis to form four spores. most well-known gymnosperm group. The single surviving spore undergoes numerous divisions by mitosis to form a multicellular female gametophyte surrounded by a thin layer of tissue called the integuments.3d). which contains . The largest family of conifers is the Pinaceae.
that help them survive in very cold and very dry environments. and produce a large amount of pollen. spruces (Picea). and modifications of the xylem. redwoods (Sequoia). and other Table 6. such as a thick cuticle.86 Plant diversity the pines (Pinus). The seed-producing female cones are woody and range in size from several millimeters to several centimeters in length. Junipers (Juniperus). cedars (Cupressus). Conifers typically produce evergreen. Male cones are small. They are native to the Northern Hemisphere. Male and female cones are produced on the same plant. Pines produce leaves in bundles called fascicles. needlelike leaves. Female cones often have unique features that can be used to identify different species. but the larches (Larix) produce deciduous leaves. where they grow in a diverse range of habitats from hot semideserts to cold mountain forests. The number of needles per fascicle can be an important trait for differentiating species.1 Group Major Groups of Living Gymnosperms Common name Estimated species Cycadophyta Ginkgophyta Coniferophyta Gnetophyta cycads ginkgos conifers gnetophytes 130–150 1 600–650 70–80 . and firs (Abies). There are approximately 100 species of Pinus. Conifer leaves have many traits. hemlocks (Tsuga). sunken stomata. papery. Another important conifer family is Cupressaceae.
however. The seeds of these families are often associated with a fleshy structure that attracts birds. The Norfolk Island pine (Araucaria heterophylla) is a common ornamental species. Some species. Sequoiadendron giganteum (giant sequoia) and Sequoia sempervirens (coast redwood) of California are some of the largest trees on Earth. Although diverse and widespread in the fossil record. The families Podocarpaceae and Araucariaceae. cycads produce male and female cones on different plants. Other species are commonly used as ornamentals in landscaping. Unlike conifers. produce fragrant wood that is used in making chests and closets. particularly in Juniperus. predominantly beetles.nonflowering Seed Plants 87 members of this family are highly valued for their wood. Cycads produce large leaves that are often mistaken for palms. After pollination. are common in the Southern Hemisphere. which transfer pollen from male to female cones while feeding on pollen and other cone parts. Like all gymnosperms. Ginkgos Ginkgophyta evolved 260 million years ago. They were an extremely diverse group. The monkey puzzle tree (Araucaria) produces some of the largest trees in southern tropical forests. They are pollinated by insects. Cycads Cycadophyta is a very old lineage of tropical and subtropical plants that evolved 290 to 248 million years ago. only one species. but have since dwindled to approximately 130–150 species in 11 genera. Ginkgo . which is used extensively in the construction industry for shingles and siding. cycads reproduce using cones. the pollen tube grows into the ovule and releases flagellated sperm that swim to the egg for fertilization. Cupressaceae is an old family whose lineage dates back 248 to 206 million years. The conifers listed previously are predominantly found in the Northern Hemisphere. on the other hand.
Comparisons of living plants to fossils show that this species has changed very little during the past 100 million years. Male and female cones are borne on separate trees. Once the pollen tube contacts the archegonium. Ginkgos are attractive trees. whose extract is commonly used as a memory enhancer. the pollen grains form highly branched pollen tubes that grow throughout the ovule tissue. After pollination.4). it . Their deciduous fan-shaped leaves turn a brilliant yellow in autumn. Ginkgo biloba is an ancient gymnosperm species.4 Shown above are Ginkgo biloba leaves and female cones. biloba (ginkgo or maidenhair tree).88 Plant diversity Figure 6. still survives (Figure 6.
Ephedra (Mormon tea) has approximately 40 species.5). bursts and releases the flagellated sperm that swim to the egg for fertilization. in 1994. Gnetum. Hence. Structural and genetic data strongly support Gnetophyta as a monophyletic group. an unknown tree species was seen in a forest in China. Plants in the genus Gnetum are woody tropical vines whose leaves resemble the broad leaves of angiosperms. living ginkgo trees were "discovered" to Westerners by Engelbert Kaempfer. They are typically shrubby plants with jointed photosynthetic stems and small. these trees were identified as dawn redwoods. In 1948. This lineage contains three genera: Welwitschia. The fleshy female ginkgo cones are infamous for their stench. In 1691. most ornamental plantings consist of male trees. Welwitschia mirabilis. most of which grow in the arid regions of the western United States and Mexico (Figure 6. Finally. is the lone member of this genus. which acts as a stimulant and can be used to treat allergies and respiratory disorders. The remaining genus. scalelike leaves. 39 trees of a gymnosperm species (Wollemia nobilis. . There are approximately 30 Gnetum species. described at the beginning of this chapter. In 1941.nonflowering Seed Plants 89 Living Fossils Paleobotanists recognized species of ginkgos and dawn redwoods from fossil records in which they were very abundant. Ephedras produce the chemical ephedrine. previously believed to be extinct. and Ephedra. Araucariaceae) thought to be extinct were found growing in a remote forest in Australia. resembling a combination of old cheese and feet. Gnetophytes Gnetophytes are quite distinct in appearance from one another and other gymnosperms. who found them growing in the temple grounds of Buddhist monks in China and Japan.
90 Plant diversity Figure 6. commonly referred to as Mormon tea. such as Arches National Park in Utah (above). Mormon tea was used by Native Americans to make a stimulating drink. .5 Ephedra. are shrubby plants that grow in arid environments.
. It is a member of a group referred to as the progymnosperms. however. however. In gnetophytes. Most important. This process of two fertilization events is similar to the one in angiosperms. Several diverse lineages of seed-producing plants evolved during the 65 million years that followed. and may suggest a common ancestor between gnetophytes and angiosperms. much the same way that modified leaves are associated with flowers. but it may provide some nourishment to the other developing embryo. woody plant. Other progymnosperm fossils have features indicating that they evolved from seedless vascular plants. For example. The oldest known gymnosperm fossils are of a plant in the genus Archaeopteris. One group called seed ferns had fernlike leaves that produced seeds at their tips. one sperm fertilizes the egg and the other fuses with a non-egg cell in the female gametophyte. oRIGIns anD ReLaTIonshIPs oF GymnosPeRms Fossil evidence indicates that seed plants first evolved approximately 365 to 380 million years ago. which means "before the gymnosperms. the pollen grain produces two sperm cells. only one of which fertilizes the egg. Seed plants evolved from these progymnosperm ancestors. It had leaves similar to fern fronds and produced seeds in sporangia attached to the branches. Some structural data suggest." Archaeopteris was a treelike. modified leaves called bracts are often associated with male and female gnetophyte cones. Likewise. In all other gymnosperms. male cones produce pollen in structures that are similar to anthers found in flowers. This second fertilization forms a short-lived embryo that eventually degenerates. that gnetophytes are more closely related to pines and are not ancestors to the angiosperms.nonflowering Seed Plants 91 Gnetophytes are of particular importance to botanists because they share interesting similarities with flowering plants. the reproductive process of gnetophytes is very similar to that of angiosperms.
Although they have lost some of their original diversity. current structural and genetic data suggests that angiosperms diverged from the gymnosperms lineage very early. and ginkgos evolved 248 to 206 million years ago and diversified 206 to 144 million years ago. were dominant plants before that time. The presence of flagellated sperm in these two groups also indicates that these are older gymnosperm lineages. Cycadeoids are interesting because they are the only gymnosperm lineage to produce cones containing both male and female structures. but they. the cordaites (Cordaitales). each with its own strengths and weaknesses. some botanists have concluded that gnetophytes are the gymnosperm lineage that shared the most recent common ancestor to angiosperms because of their similar fertilization process (called the anthophyte hypothesis). Cycads and ginkgos are closely related basal lineages in the gymnosperms. and that gymnosperms continued to diversify (called the gne-pine hypothesis). Although there are compelling reasons that support this conclusion. Cycadeoids (Bennettitales) are another extinct gymnosperm lineage. this highly successful group of plants has existed for more than 145 million years.92 Plant diversity Another important group. Cycadeoids became extinct approximately 65 million years ago. along with lycophytes and calamites. but the two other lineages exist still today. Because some of the earliest gymnosperm lineages are known only from fossils. As described earlier. Seed ferns and cordaites became extinct 290 to 248 million years ago. cycads. there is uncertainty about the relationships among them. contained trees and shrubs that resembled modern conifers. Cycadioids. depending upon the data used to construct the phylogeny. and Pinaceae conifers and gnetophytes evolved from a common ancestor. . Several different phylogenies have been proposed for living gymnosperms. Nonpine conifers comprise one remaining lineage.
Gymnosperms have significant economic value. summaRy Gymnosperms are seed-producing vascular plants. the hypothesis is the phylogeny developed by a systematist. which can be converted into a variety of commercial products including turpentine and rosins. diverse groups that have since become extinct. In systematics. and cycadeoids. Seeds and pollen are produced in cones composed of sporophylls or cone scales.nonflowering Seed Plants 93 Every tree is a Hypothesis A fundamental component of the scientific method is the developing and testing of hypotheses. Gymnosperms arose from seed-producing ancestors that evolved more than 365 million years ago. Because it is impossible to actually observe the entire evolutionary history of a group of plants. ginkgos. water availability. they also shape their environment by affecting soil. and gnetophytes are the four living gymnosperm lineages. such as piñon pines and junipers. such as the seed ferns. In the past. Gymnosperm lineages. VaLue oF GymnosPeRms Gymnosperms are ecologically important plants that are domi- nant species in many ecosystems worldwide. and paper pulp production. are even grown for food and flavorings. and temperature. . Other systematists can then collect and analyze additional data to test the relationship proposed in the original phylogeny or propose new relationships. In addition to providing habitat and food for other organisms. were large. A wide variety of species are used in landscaping. cycads. Conifers. A few gymnosperms. pine resins called naval stores were used as a waterproofing agent for wooden ships. systematists develop a phylogeny based on their interpretations and conclusions from the data they collected. lumber. Pines in particular are tapped for resins. Other species are grown for fuel. cordaites.
Flowering Plants The angiosperms 94 .
—Charles Darwin (1809–1882) English naturalist .The rapid development . . . of all the higher plants within recent geological times is an abominable mystery.
have associate red roses with true love. lilies with France.. By 60 million years ago. the eminent botanist Sir Joseph Hooker. Throughout history." Acorns are a symbol of immortality. Say it With Flowers "O.000 species of angiosperms reveals an astonishing array of flower and fruit structures and modifications. Several nations are also associated with flowers: peonies with China. and thistles with Scotland. Angiosperms made their first appearance in the fossil record approximately 135 million years ago. Another evolutionary advantage of angiosperms is their diversity of growth forms and vegetative traits. 96 . and dominance of the landscape in the history of Earth.Flowering Plants The angiosperms The passage on the previous page is from a letter written by Charles Darwin to his colleague. flowers and fruits have been associated with emotions and other things in what is called "The Language of Flowers. A survey of the more than 250. Angiosperms range from minute aquatic plants. The "abominable mystery" Darwin referred to was the sudden and dramatic appearance and diversification of angiosperms in the fossil record. Foxgloves represent insincerity. Yellow poppies and corn symbolize success and riches.. a majority of the modern angiosperm families that exist today were well established.. The success of the angiosperms was made possible largely through the unique features that resulted from the evolution of flowers and fruits. Angiosperms then underwent a rapid proliferation and diversification 70–100 million years ago. and millions of other romantics past and present. Fossils of other major groups of plants show a pattern of lineages appearing gradually and diversifying slowly over the course of hundreds of millions of years. diversification." The Scottish poet Robert Burns. my love's like a red. No other group of plants has shown such rapid evolution. red rose.
. and one or more carpels. to a giant quaking aspen (Populus tremuloides) clone that covers 106 acres and is the largest organism on Earth. petals. Angiosperms are an important resource to humans. Their ability to adapt to their environment has allowed angiosperms to have an amazing impact on the ecology and evolution of life on Earth. stamens.1 A typical flower consists of sepals. and refers to the fact that Figure 7.Flowering Plants 97 such as watermeal (Wolffia). as they have both practical use and cultural significance. The FLoWeR The word angiosperm comes from the Greek words angeion ("vessel") and sperma ("seed").
1).2). The presence of flowers that produce these seed-enclosed fruits is a defining characteristic of angiosperms. which is supported on a stalk called the filament. The innermost whorl of a flower is the gynoecium (meaning "female house"). The outermost whorl. A gynoecium may consist of one or more carpels. The stamens make up the third whorl. which is composed of the carpels. The petals of the flower make up the next whorl. they are often brightly colored. An inflorescence can be composed of a single .98 Plant diversity angiosperms produce seeds from ovules that are completely enclosed in sporophyte tissue. the angiosperm vessel is the wall of the ovary that encloses the seed. which produce the gametes required for sexual reproduction. Flowers consist of four parts (sepals. which cover and protect the developing flower bud. which is known as the androecium (meaning "male house"). stamens. Sepals and petals that cannot be distinguished from one another. which is called the corolla. This is in contrast to gymnosperms. The carpel is also called the pistil. All four whorls attach to a structure at the base of the flower called the receptacle . The calyx and corolla are called the sterile whorls because they do not produce gametes. as is the case with tulips and cacti. which produce seeds from a bare ovule. The stamens and carpels make up the two fertile whorls. attracting pollinators for sexual reproduction. or calyx. leaflike sepals. are called tepals. petals. and ovary. Pollen containing the male gamete (sperm) is produced in the anther of the stamen. Flowers are grouped together on a plant to form an inflorescence (Figure 7. Petals may resemble leaves. and carpels) that are arranged into four groups called whorls (Figure 7. is composed of green. The ovary of the gynoecium eventually matures to form a fruit containing one or more seeds. Specifically. but unlike leaves. style. Carpels are made of a stigma. A gynoecium composed of two or more carpels fused together is a compound pistil.
Inflorescence refers to the way in which individual flowers are arranged on the stem. or any number of different multiflowered inflorescences.2 Shown above are the basic types of inflorescences. The stalk that supports an inflorescence. is called the peduncle. whether multi-flowered or solitary.Flowering Plants 99 Figure 7. . flower (solitary inflorescence). The stalk that supports an individual flower within a multi-flowered inflorescence is called the pedicel.
The generative cell divides to form two sperm cells. The seedling develops into a mature plant that will eventually form flowers. It begins with the germination of a seed. the female gametophyte is physically attached to. form the ovule. . This tube grows through the style toward the ovary. Within the carpel. where the sporophyte is attached to. Most flowers contain both stamens and carpels. Three of the haploid spores degenerate while one divides three more times to produce the female gametophyte. The growing pollen tube is the male gametophyte. Ovules are enclosed and attached to the sporophyte tissues of the ovary. particularly the female gametophyte. These seven cells and eight nuclei make up the mature female gametophyte and. This is exactly the opposite of what occurs in bryophytes. and nutritionally dependent upon. and nutritionally dependent upon a much larger gametophyte. When the pollen grain germinates on the stigma. with the integument layers around it. the tube cell controls the growth of the pollen tube. Within the anther on the stamen. The angiosperm female gametophyte is composed of seven cells. which is the sporophyte generation. spore mother cells undergo meiosis to form haploid spores. stamens and carpels are produced in separate flowers on the same or different plants. Three cells are the antipodals and two cells called the synergids are next to the egg. carrying with it the generative cell. Thus. A key feature of the angiosperm life cycle is the reduction of the gametophyte stage.100 Plant diversity anGIosPeRm LIFe cycLe The life cycle of a lily serves as a good example of the angiosperm alternation of generations. spore mother cells undergo meiosis to form four haploid spores. the mature sporophyte. The large central cell contains the two haploid polar nuclei. Each spore develops into a pollen grain containing a tube cell and a generative cell. In some angiosperms. and elaboration of the sporophyte.
Flowering Plants 101
Pollination by deception
Flowers use different combinations of color, scent, and shape to attract pollinators. Some of the most specialized flower pollinator relationships involve orchids, whose flowers mimic the color, shape, and even scent of females in the bee and wasp species that pollinate them. Male bees and wasps, lured in by the false promise of a mate, inadvertently transfer pollen from one flower to another. Some arums (plants of the family Araceae) use a similar strategy, mimicking the stench of rotting meat. Flies, seeking a place to deposit their eggs, pollinate the flowers.
DouBLe FeRTILIzaTIon
When the pollen tube reaches the ovule, it releases the two sperm cells. One sperm cell fuses with the egg to form the zygote that will eventually become the next sporophyte. The other sperm cell fuses with the two polar nuclei to form the endosperm, which provides food for the developing zygote. This double fertilization is a unique feature of the angiosperm life cycle. Following the formation of the zygote and endosperm, the ovule develops into the seed that contains the plant embryo and food reserves, which may be in the form of endosperm or sugars and starches stored in modified leaves called cotyledons. Ripe ovary tissues surrounding the seed form the fruit. Ultimately, the seed is dispersed from the plant through a variety of different mechanisms. Some fruits are fleshy and contain sugars, lipids, or other substances to entice animals to eat the fruit and internally transport the seed until it passes through the digestive tract. Others have hooks, barbs, or other devices that attach to the outside of animals to disperse the seed. Once dispersed, the seed will germinate and form the next sporophyte.
majoR anGIosPeRm GRouPs
In 1703, English botanist John Ray divided angiosperms into monocots (plants whose seeds have one cotyledon) and dicots
102 Plant diversity
Table 7.1
Major Groups of Living Angiosperms
Common name Estimated species
Amborellaceae Nymphaeaceae Autrobaileyales Nymphaeaceae, Illiciaceae Magnoliopsida* Liliopsida Magnoliopsida* magnoliids monocots eudicots 9,000 70,000–72,000 175,000–180,000 basal angiosperms 170
* Magnoliopsida is the traditional name given to dicots. At present there is no ICBN name for the separate magnoliid or eudicot clades.
(plants whose seeds have two cotyledons). Botanists have traditionally followed this classification and continued to divide angiosperms into the Magnoliopsida (dicots) and Liliopsida (monocots) based on a variety of traits, such as the arrangement of vascular bundles (Figure 7.3) and features of roots, leaves, and flowers. Recent studies, however, have shown that the dicots are an artificial grouping of several different lineages. Some plants previously classified as dicots are actually ancient angiosperm lineages that are now collectively referred to as the basal angiosperms (Table 7.1). This group consists of several families, including the Amborellaceae, Nymphaeaceae, and Illiciaceae. The remaining angiosperms are now referred to as the core
Flowering Plants 103
This group includes three monophyletic lineages: magnoliids, eudicots, and monocots. The magnoliid clade contains several ancient angiosperm families, including the a
Figure 7.3 Cross-sections of monocot and dicot stems reveal the differences in vascular bundle arrangement. Vascular bundles are arranged in a ring in dicots (a), but scattered in the monocot stem (b).
Monocots account for approximately 22% of all angiosperms. four-merous.2 Differences Between the Three Core Angiosperm Groups Monocots Magnoliids Eudicots Trait Cotyledons Vascular bundle arrangement in stem Leaf vein pattern pinnate Number of flower parts Openings in pollen grains 1 scattered parallel three-merous 1 2 ring pinnate many 1 2 ring palmate. magnoliids. natural group that contains about 75% of all dicot species. monocots are still recognized as a single lineage that descended from a common ancestor. Eudicots share a common feature that is not found in any other flowering plants: They have three openings in their pollen grain walls.2). Eudicots (true dicots) make up a large. Table 7. five-merous 3 . Beyond this difference. Despite changes in our understanding of dicots. laurels (Lauraceae). magnoliids and eudicots share many other features (Table 7.104 Plant diversity magnolias (Magnoliaceae). and black peppers (Piperaceae). spicebushes (Calycanthaceae). basal angiosperms. All other plants (gymnosperms. and monocots) produce pollen grains that have only one opening in their walls.
Tropical forests. are often dominated by trees from a multitude of different families. such as roses.) and cinquefoil (Potentilla). and figs (Moraceae). members of the mustard family (Brassicaceae) produce flowers with four sepals.4).Flowering Plants 105 Significant differences exist between the floral structures of eudicots and monocots. The rose family (Rosaceae) is well known for its ornamental species. The bean family (Fabaceae) is one of the largest angiosperm families. including dipterocarps (Dipterocarpaceae). laurels (Lauraceae). ornamentals. The . Monocot flowers. which refers to the unique fruit produced by species in this family. and blackberries. strawberries. plums. In eudicot flowers. and pears (Pyrus). are three-merous. fibers. Species in the rose family (Rosaceae). hickories (Juglandaceae). consequently. Angiosperms also include many important resources that humans depend on for a variety of purposes. such as irises. however. and a pistil with three carpels. three petals. and cherries (all in the genus Prunus). and peaches. For example. three or six stamens. Members of Fabaceae are also called legumes. four petals. like roses (Rosa sp. and tulips. with three sepals. Many of these families also provide timber and other resources for humans. Angiosperms provide food. and maples (Sapindaceae) are major components of forests in many temperate areas. and four stamens. and also for its edible species (Figure 7. Oaks (Fagaceae). have flowers with five sepals and five petals. like apples (Malus). play a major role in the ecological dynamics that maintain a healthy planet. lilies. Trees in these families support numerous other life forms in forest ecosystems by providing food and habitats. the parts of the different floral whorls are typically in multiples of four (four-merous) or five (five-merous). and a wide array of chemicals. ecoLoGIcaL anD economIc VaLue Angiosperms are dominant components of terrestrial environments worldwide and.
soybeans (Glycine max). making this an agriculturally important family.106 Plant diversity a b c d Figure 7. peaches ready to be picked (b). Species such as beans (Phaseolus vulgaris). and lentils (Lens culinaris) contribute to the diets of humans and wildlife worldwide. ripe cherries (c). Pictured above are two ripened apples (a). symbiotic relationships between legumes and nitrogen-fixing soil bacteria give legume seeds (beans and peas) a high protein content. . field peas (Vicia faba).4 The rose family includes many edible fruits. and fresh pears (d).
such as cheat grass (Bromus tectorum) and Johnson grass (Sorghum halapense). and papermaking. mums (Chrysanthemum).000 species. as well as aggressive. belladonna (Atropa). Bamboos (Bambusa) are grasses that have a wide range of uses. lavender (Lavandula). savannas. and bee balm (Monarda) are popular ornamentals. Catnip (Nepeta). with more than 25.Flowering Plants 107 The mint family (Lamiaceae) includes many culinary herbs and plants renowned for their perfumes. textiles. including dahlias (Dahlia). The flavors and scents of plants in the mint family come from glands on the leaves. Basil (Ocimum basilicum). Important edible plants. oil. which produce aromatic oils. and rice (Oryza sativa) providing 50% of human caloric intake. and tundra ecosystems. and thyme (Thymus) are valued herbs in Lamiaceae. Other species. The poisons are often powerful alkaloids. Nine of the top 20 crop species are grasses. mint (Mentha). are invasive species that have a detrimental effect on native vegetation. Tobacco (Nicotiana). such as dandelion (Taraxacum officiale) and Canada thistle (Cirsium arvense). including construction. with corn (Zea mays). oregano (Origanum vulgare). Hot peppers (Capsicum) get their heat from the alkaloid capsaicin. This monocot family serves as the foundation of food webs and other processes in prairies. The grasses (Poaceae) account for approximately 17% of all angiosperms. and flowers. including tomato (Solanum lycopersicum) and potato (Solanum tuberosum). This family also contains commercially grown ornamentals. which is grown for its seeds. Grasses can be found in most other ecosystems as well. . wheat (Triticum aestivum). The sunflower family (Asteraceae) is the largest of all eudicot families. such as the annual sunflower (Helianthus annuus). coleus (Plectranthus). sage (Salvia officinalis). patchouli (Pogostemon cablin). noxious weeds. and jimsonweed (Datura) produce alkaloids with narcotic effects. and marigolds (Tagetes). The nightshade family (Solanaceae) contains many poisonous plants. which have a range of effects. rosemary (Rosmarinus officinalis). are also in this family. It contains many commercially important species.
The Iridaceae includes irises (Iris). Photographed above are the white lily (a). The anthers from Crocus sativus . gladiolus (Gladiolus).108 Plant diversity a b c Figure 7. and the harlequin "dancing lady" orchid (c). purple iris (b). crocus (Crocus).5 The lilies. showy flowers. also known as a butterfly plant. The irises (Iridaceae). colorful petals in their flowers (Figure 7. irises. and orchids produce bright. orchids (Orchidaceae). and lilies (Liliaceae) are often called the "showy monocots" because of the bright.5). and blue-eyed grass (Sisyrynchium).
Magnoliaceae is an ancient family. including onion (Allium cepa). who suggested that Amentiferae. that neither of these families are representative of the oldest type of angiosperm. It was a simple plant whose flowers had no sepals or petals. and the order Illiciales are the oldest living lineages of flowering plants. where they form close relationships with the organisms that pollinate their flowers. but it is not the oldest. just like the more primitive gymnosperms. Recent genetic analyses have shown. garlic (Allium longicuspis).Flowering Plants 109 are the source of the spice saffron. Orchids are the largest angiosperm family. these ancient groups form . a group in their classification. Nymphaeaceae. Other researchers concluded that families such as Magnoliaceae (magnolia family) and Ranunculaceae (buttercup family) were the most primitive because their flowers contain many parts. Trimeniaceae. Collectively. and Ranunculaceae has been shown to be a member of the eudicots.000 species. The oldest complete fossil plant is in the genus Archaefructus that lived more than 125 million years ago. Currently. There are terrestrial orchids as well as many epiphytes. many botanists agree that the families Amborellaceae. oRIGIns anD ReLaTIonshIPs oF anGIosPeRms The oldest angiosperm fossils are flowers and pollen that are 130–140 million years old. This conclusion was based on the fact that many of these trees are wind pollinated. Liliaceae contains ornamentals including lilies (Lilium) and tulips (Tulipa). but numerous stamens. plants that grow on the stems and branches of trees. and chives (Allium schoenoprasum). There are several edible lilies. with more than 30. One of the first hypotheses about the origins of flowering plants was developed by Engler and Prantl. was the most primitive angiosperm group. simple flowers that have few parts and simple pollination mechanisms. These groups produce small. Orchids are particularly diverse in the tropics. however.
Fruit size. Many studies have indicated that it is likely the living descendent of the oldest angiosperm lineage on Earth. A typical Rafflesia flower can be up to 3 feet (1 m) across and weigh as much as 25 pounds (11 kg). Separate male and female flowers are attached to a central column that can be 3 to 6 feet (1 to 2 m) tall. and scents to attract pollinators. A huge modified leaf surrounding the column gives the spadix the appearance of being a single large flower. The titan arum (Amorphophallus titanium) produces the largest inflorescence. and eudicots diverged as separate lineages approximately 100 million years ago. fruits provide a food reward to animals that eat a fruit and disperse the enclosed seeds. shape. colors. magnoliids. The evolution and diversification of these insect and bird pollinators is linked to that of the angiosperms. . and color have evolved in response to natural selection mediated by Big Flowers The brownish-orange flowers of the giant rafflesia (Rafflesia arnoldi ) are the largest single flowers of any angiosperm. but they combine to form a special type of inflorescence called a spadix. Fossil evidence also indicates that the first angiosperms had small. Flowers also frequently provide a food reward of pollen or nectar to pollinators in return for the service of visiting flowers and transferring pollen.110 Plant diversity the basal angiosperms. Flowers enabled plants to use different shapes. The flower undoubtedly is a primary reason for this success. nondescript flowers with few floral parts. Its flowers are very small. anGIosPeRm success Angiosperms have evolved and dominated the terrestrial environment like no other group of plants. Fossil and genetic data indicate that monocots. The species Amborella trichopoda (Amborellaceae) is a shrubby plant that grows in the cloud forests of New Caledonia. Like flowers.
angiosperms have accelerated the process. Changes in the life cycle have also promoted angiosperm evolution. thereby speeding their response to natural selection and accelerating the evolution and spread of adaptive traits. Pollination. summaRy Angiosperms are vascular plants that produce seeds from flowers and enclose the seeds in a fruit. gymnosperms. can take as long as two years to progress from pollination to the release of the mature seed. monocots. Angiosperms are also the only seed plants to have evolved the annual life cycle in which a plant completes its life in one growing season. angiosperms can reproduce more quickly. and eudicots. There are three major groups of angiosperms: basal angiosperms. The flower and fruit are key traits that allowed angiosperms to interact with animal pollinators and seed dispersers and. This acceleration may be due to the nutritional benefits of the endosperm for the developing embryo. consequently.Flowering Plants 111 the animals that eat and disperse the seeds. and they dominate the terrestrial environment. fertilization. Many species in these groups are ecologically and economically important. . undergo extensive diversification. Angiosperms are the most recently evolved group of plants. By shortening different aspects of their life cycle. Angiosperms have evolved an array of mechanisms to disperse their offspring. While the other seed plants. and maturation of the seed can occur within a matter of days or months.
Artificial classification system A system of grouping organisms that is based on arbitrary features rather true evolutionary relationships. Basal angiosperms A name given to the most primitive angiosperm lineages. and other primitive life forms. Angiosperms Plants that produce flowers and whose seeds are contained within a fruit. Alternation of generations A life cycle that alternates between a multicellular haploid generation and a multicellular diploid generation. 112 . Archegonia The female reproductive structures that produce and protect the egg. Androecium The male parts of a flower. Arbuscules Specialized structures formed by mycorrhizal fungi inside a plant cell that enable the plant and fungus to exchange nutrients Archaea The kingdom of prokaryotic unicellular organisms containing blue-green algae. Bacteria A group of unicellular.Algae A general term for photosynthetic members of the kingdom Protista. Asexual reproduction Formation of offspring that does not involve the joining of egg and sperm. Ascocarp The fruiting body of an ascomycete. Annulus A thickened band of cells on a fern sporangium. methane-producing bacteria. Autotrophs Organisms capable of synthesizing its own energy. prokaryotic organisms. Animalia The animal kingdom. Anatomy The study of an organism's structure. Ascus (plural: asci) A saclike cell in which ascomycetes form spores. Anther Floral structure in which pollen is produced. which is involved in the dispersal of spores. Antheridia Male reproductive structures that produce and protect sperm. Alkaloid A type of chemical produced by certain plants that is made out of nitrogen and can be toxic when ingested. Antipodals The three cells of the female gametophyte that are clustered at the end opposite the egg.
central cell The cell in the angiosperm female gametophyte that contains two haploid nuclei. cellulose The main component of cell walls in plants. clade A group consisting of an ancestor and all of its descendants. Basidiocarp The fruiting body of a basidiomycete. calamites Ancient group of horsetails. Bracts Modified leaflike structures that can be part of a flower or fruit. chromosomes The organized structures of DNA in a cell. 113 . hornworts. Blades The flattened photosynthetic regions of a leaf or algae. Biodiversity The diversity of life on Earth. which have slight differences in the wavelengths of light they absorb. chloroplasts Structures within plant cells that contain the enzymes and pigments necessary for photosynthesis. and quillworts. calyx The outermost floral whorl consisting of all of a flower's sepals. Bryophytes Non-flowering plants that include mosses. There are two types of chlorophyll. Bud Small embryonic floral or vegetative shoots. carpels The ovule-encasing structures that make up the gynoecium. carotenoids A class of yellow and orange pigments. Brown algae Group of multicellular algae usually found in marine environments. a and b. it becomes endosperm after fusion with second sperm nucleus. Binomial nomenclature The system developed by Linnaeus in which each species is given a name consisting of two words: the genus name and the species name.Basidium (plural: basidia) The club-shaped structure in which basiomyce- tes form spores. chlorophyll A green pigment responsible for capturing the light used in photosynthesis. liverworts. chitin A substance that forms the cell walls of certain fungi. capsule A spore-containing structure of the moss sporophyte.
cone scale An individual unit of the gymnosperm strobilus. eudicots. deciduous A plant that loses its leaves during autumn or the dry season. corm A dry underground structure found in perennial plants such as gladiolus. crozier The coiled leaf of a fern. classification The process of organizing groups into a hierarchical system. typ- ically found in gymnosperms and other groups of nonflowering plants. dicots A general term given to angiosperms whose seeds produce two cotyledons. crustose A lichen growth form that resembles a crust on the substrate upon which it grows. dichotomous key A list of paired. cuticle A waxy.cladistics The system of grouping organisms based on an analysis of their primitive and advanced traits. now divided into two groups. cone A reproductive structure that produces either pollen or seeds. dendrograms Treelike diagrams that illustrate relationships. the basal angiosperms and the eudicots. cotyledon A leaf that provides nourishment to the plant embryo during germination. 114 . characteristic of the sporophyte generation. compound pistil A gynoecium composed of two or more carpels fused together. corolla The (usually) conspicuously-colored flower whorl consisting of all of the flower's petals. contrasting statements used to iden- tify an unknown organism by the process of elimination. common name The unofficial name given to a plant by those who live near it. protective layer on the outer surfaces of leaves. core angiosperms Groupings that include three monophyletic lineages: magnoliids. and monocots. dikaryotic Cells in fungi that have two haploid nuclei. diploid Having two full sets of chromosomes in each cell.
including sperm. Ethnobotanists Scientists who study the ways in which indigenous peoples use plants. Fertilization The joining of egg and sperm in sexual reproduction. wherein one sperm fuses with the egg to form the zygote and a second sperm fuses with the polar nuclei to form the endosperm. Five-merous A flower that contains parts in multiples of five. Flavonoids A class of pigments found only in plants and a few algae. Evergreen A tree whose leaves can be shed at any time of year. characteristic of angio- sperms. Float The inflated part of a kelp body. Evolution A change in genetically-based characteristics of a species throughout time. Eukaryotic Organisms whose cells contain nuclei and membrane-bound organelles. Eudicots The largest group of angiosperms. domain The taxonomic level above kingdom. Filament The stalk of a stamen. Field guide A book that contains simple descriptions and illustrations of plants in an area. they have two cotyledons and three openings in their pollen grains. Fertile whorls The whorls of a flower that produce gametes.diversity A measure of the number and relative proportion of different species in a community. double fertilization A two-fertilization event. particularly for medicinal purposes. Endosperm The tissues formed during a double fertilization event that nourish the growing angiosperm embryo. Flagella Tail-like structures that propel many eukaryotic cells. Epiphytes Nonparasitic plants that grow on trees. but never all at once. Fiddlehead See Crozier. Fascicles Bundles of pine needles. 115 .
Gemmae (singular: gemma) Small masses of vegetative tissue that form on the upper surface of a thallus that can be dispersed for asexual. Gymnosperms Plants that reproduce using cones and bear exposed "naked" seeds (that is. Germination The resumption of growth by a dormant spore. not contained in fruits). or pol- len grain. 116 . vegetative reproduction. illustrations. Gills The plates on the underside of the caps of basidiomycete fungi. gamete-producing stage in the alternation of generations. petals. seed.Flora A guide with descriptions. Four-merous A flower that contains parts in multiples of four. Green algae The group of algae that gave rise to plants. Haploid Having only one set of chromosomes. Fruit The mature seed-containing ovary (or group of ovaries) of angiosperms. Food webs An interlocking system of producers and consumers in an ecosystem. Fronds Fern leaves. Foliose A lichen growth that resembles leaves. stamens. Gynoecium The collective term for all of the carpels in a flower. Genus The taxonomic rank below family and above species. Generative cell The cell in a pollen grain that divides to become two sperm cells. distributions maps. and keys that allow the user to identify plants of a particular geographical area. and carpels. either sperm or egg. Fruticose A lichen growth form that is highly branched and erect. Fungi The kingdom of organisms that have cell walls and obtain their food through absorption. Flowers The reproductive structures of angiosperms composed of sepals. Gamete A haploid reproductive cell. Gametophyte The haploid.
Leaves The flattened photosynthetic parts of a vascular plant. Lichen Organism that results from a symbiotic relationship between a fun- gus and an alga. Hyphae (singular: hypha) Fungal filaments. Mating types Genetically different forms of algae capable of sexually reproducing with one another. Herbarium A place where preserved plant materials are stored for study. dried plant specimens are mounted. Kingdom The taxonomic level below domain. Heterotrophs Organisms that must obtain energy by consuming other animals. indusium A protective flap that covers immature sori in ferns. 117 . integuments Protective outer layers that surround the sporangium of an ovule.Herb A nonwoody plant. Legumes Fruits that are characteristic of the bean family. they typically provide information such as the plant's scientific name and where and by whom it was collected. inflorescence A cluster of flowers close to one another on a stem. international code of Botanical nomenclature (icBn) The internationally agreed upon set of rules that govern the naming of plants. Holdfast Part of the algal body that attaches the alga to the substrate. Heterospory The production of two types of spores: microspores that give rise to male gametophytes and megaspores that give rise to female gametophytes. international Botanical congress The governing body that establishes rules on botanical nomenclature. the primary com- ponent of wood. Lignin A component of the hardened cell wall in xylem. Homospory The production of one type of spore. Herbarium sheets Pieces of paper upon which pressed. Hydroids Primitive water-conducting cells in mosses. Leptoids Primitive food-conducting cells of mosses.
Megaphylls Large leaves with many veins. Megasporangium A structure in which spores are formed that will
become a female gametophyte.
Megaspores Spores that give rise to the female gametophyte. Meiosis The process whereby a diploid cell divides twice to produce four
haploid cells.
Microphylls Generally small leaves with a single vein. Micropyle A small opening in the seed plant ovule that the pollen tube
enters for fertilization.
Microsporangium A structure in which spores that will become the male
gametophyte are formed.
Microspores Spores that will give rise to the male gametophyte. Mitosis The process whereby one diploid cell divides once to produce two identical diploid cells. Monocots Angiosperms whose seeds contain a single cotyledon. Monophyletic group A group composed of an ancestor and all of its
Morphology The study of the structure and form of organisms. Mutualism A relationship that benefits both participating species. Mycelium A mass of fungal hyphae. Mycology The study of fungi. Mycorrhizae Fungi that engage in symbiotic relationships with plant roots. natural classification system A system of grouping organisms that is based on their evolutionary relationships. natural selection A process of evolutionary change that occurs when
genetic change produces individuals with greater reproductive success or greater survival.
nitrogen fixing Process of converting nitrogen from a gas into a biologi-
cally useful form.
nucleus Part of a eukaryotic cell that contains DNA. 118
organelles Small, specialized structures within a eukaryotic cell. ovary The enlarged, seed-producing portion of a flower that, after fertilization, becomes a fruit. ovules Structures in seed plants that contain the female gametophyte. Pedicel The stalk of a single flower in an inflorescence. Peduncle The stalk of a solitary flower or inflorescence. Perennials Plants that live for more than two years and typically reproduce repeatedly throughout their lives. Petals The parts of a flower that are often brightly colored. Petiole The stalk of a leaf that attaches the blade to the stem. Phloem Tissue that transports sugars and other products of photosynthe-
sis throughout the vascular plant body
Photoautotrophs Organisms capable of forming their own energy
resources through photosynthesis.
Photosynthesis The process through which plants convert the energy in
light into sugars and oxygen.
Phycobilins A group of reddish pigments found in red algae and blue-
green algae.
Phycology The study of algae. Phylocode A nomenclature system that has no hierarchical rankings and recognizes only clades. Phylogeny The evolutionary history of an organism or group of
Pistil The collective term for the female parts of a flower. Plantae The plant kingdom. Polar nuclei The two nuclei located in the female gametophyte of angio-
sperms, which fuse with a sperm to form the endosperm.
Pollen A structure containing the sperm cells in angiosperms and gymno-
Pollen tube A tube that develops from a pollen grain and carries the sperm
to the egg.
Pollination In angiosperms, the transfer of pollen from an anther to a
stigma; in gymnosperms, the transfer of pollen from a male cone to a female cone.
Pollinators Organisms that transfer pollen from one flower to another. Polynomial An outdated system of assigning a name of multiple parts to
one species.
Progymnosperms A group of now-extinct plants that gave rise to
Prokaryotic Organisms whose cells lack nuclei and membrane-bound
Protista The protist kingdom. Protonemas The threadlike gametophytes of some nonvascular and seed-
less vascular plants.
receptacle The structure in a flower where the floral whorls attach. red algae A large group of mostly multicellular marine species that get
their characteristic color from reddish pigments in their cells.
rhizoids Primitive structures that nonvascular plants use to attach to their
Scientific name The official name for a plant, consisting of two words: the genus and the species. Seed ferns Extinct group of fernlike gymnosperms that produced seeds at the tips of their leaves. Seedless vascular plants A group of plants that includes ferns, horsetails,
and club mosses that have vascular tissue, but reproduce by spores.
Seeds Fertilized plant ovules consisting of an embryo and its food source. Sepals Leaflike outermost structures of a flower. Seta Stalk that supports the capsule in the moss sporophyte. Sexual reproduction The formation of offspring by combining egg and
Shrub A woody plant that produces several stems and is shorter that a tree. Sori The clusters of sporangia on the leaf surface of a fern. 120
Synergids Two cells located near the egg in the female gametophyte of angiosperms. Sterile jacket A layer of cells that surrounds the gamete-producing archegonium and antheridium.Spadix A special type of inflorescence found in some angiosperms. composed of anther and filament. Stamens The male parts of flowers. Spore mother cells Cells in a plant's reproductive tissue that undergo meiosis to form haploid spores. Stipe The stem of a brown algae body. that produce pollen. cumulative changes in the composition and characteristics of a plant community following disturbance. Strobilus (plural: strobili) A cone-like cluster of spore-bearing leaves. Sporophylls Modified leaves that bear sporangia. Stomata Openings in the leaf surface that allow a plant to take in and release gasses. spore-producing stage in the alternation of generations. all members of a species have the ability to interbreed and share a common evolutionary history. 121 . Sporophyte The diploid. Succession A series of predictable. pollen tubes grow through the style to reach the ovary. Symbiotic A relationship in which both individuals benefit from the inter- action and are harmed when they are not together. Species A particular type of organism that can be differentiated from other types of organisms. Sporangium A spore-producing structure. Spores Single-celled reproductive structures in bryophytes and seedless vascular plants that are capable of developing into a plant. Stigma The receptive potion of the carpel upon which pollen grains germinate. Style The carpel tissue that connects the stigma to the ovary. Sterile whorls The parts of a flower (sepals and petals) that do not pro- duce gametes.
such as kingdom or species. or leaf. Vascular bundles Strands of tissue that contain xylem and phloem. Xylem Tissue that transports water and minerals throughout the vascular plant body Zygospore A dormant spore formed in zygomycetes and some algae. tree A woody plant with a single trunk. undifferentiated into root. tracheids Elongated. three petals. thick-walled xylem cells found in most vascular plants that conduct and support. three-merous Having three sepals. tracheophytes Another name for vascular plants. tepal Sepals and petals that cannot be distinguished from one another. taxonomy The science of classifying organisms. Vegetative reproduction Asexual reproduction through the breaking off of a part of the plant body to produce a new plant. three or six stamens. Vascular cambium A localized area of cell division and growth in plants that produces new vascular tissue and contributes to increased diameter of woody stems. tube cell The cell that develops into the pollen tube in the male gameto- phytes of seed plants.Systematics The study of evolutionary relationships and diversity. Zygote The diploid first cell of a sporophyte that results from the joining of sperm and egg at fertilization. 122 . Vascular tissue Tissue used to transport water and minerals throughout the plant body. Whorl An arrangement of three or more floral parts or leaves in a circle. stem. taxon A group of organisms at any hierarchical level. thallus A simple vegetative body. and a pistil with three carpels.
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67–68 major groups of. 96 life cycle of. 39. 96 Adanson. 54. 56. 34. 12 Archaeopteris. 85 of seedless vascular plants. 34 Allergies. 15 evolution of. 54. 109–110 Amentiferae. 41–42. 13 Bacteria Kingdom. 46–47 Brunfels. 29. 34. 44–46 lichens and. 59 relationship to gnetophytes of. 58 of gymnosperms. Hieronymus. 105–109. 109–111 features of. 45 relationship of fungi to. 71 Age of Herbals. 60–61 features of. 26 Angiosperms dominant generation in. 106 Basal angiosperms. 92 Carotenoids. 107 Autotrophs. 65–66 129 . 12. 52 green. 52. 39. 70–71. 29. 56. 7–8. 59 mutualistic relationship with fungi. 66. 102.Abominable mystery. 92 Binomial nomenclature. 37. 39. 57. 76 Asteraceae. 47–48 Asexual reproduction. 68 Araucariaceae. 54. 54. 52 dominant generation in. 91 Bread mold. 96 value of. 56. 96 Calamites. 91 symbolism of specific. 44 value of. Michel. 20–21 Air pollution. 101 Ascomycota. 37. 12. 36. 21 Bryophytes ancestors of. 101–105 with moss in name. 34 Cell walls. 23 Adder's tongue ferns. 47–48 with moss in name. 56–59 sporophytes of. 52. 13 cuticles and. 100–101. 67 Artificial classification system. 46. Otto. 35 of seedless vascular plants. 73 Bracts. 45 red. 111 major groups of. 40–41 Archaea Kingdom. 57. 40 Bristlecone pines. 47 study of. 52 of fungi. Robert. 66 value of. 91 Archegonia of bryophytes. 49 Algae brown. 89 Amborellaceae. 61 Burns. 54 life cycle of. 12. 84 Brown. 12 Antheridia of bryophytes. 23 Arums. 13 Carrageenan. 29. 46. 57. 87 Arbuscular mycorrhizal fungi. 37. 15 evolution of. 12 mutualistic relationship with algae. 109 Anatomy. 67. 40. 47 Beans. 98. 42–43. 105–106 Bennettitales. 46–47 evolution and. 109–110 Basidiomycota. 58 of seedless vascular plants. 35–36 Angiosperm Phylogeny Group. 45. 21 Bracken ferns. Robert. 110–111 Animalia Kingdom. 23 Bock. 96–99 first appearance of. 81 Brown algae.
85 Cones of club mosses. 101–102 Croziers. 86–87 Cuticles. 34. 12. 45 Chloroplasts. See photosynthesis Engler. 43 Dendrograms. 29. Dioscorides). 11. 49 Cupressaceae. 73 Cycadeoids. 87 of ginkgos. 36–37 Dioscorides. 36. 40.Charophytes. 22–23. 89 Epiphytes. 4. 45–46 Cheng Lei Pen Ts'ao (The Materials of Medicine Arranged According to Pattern. 20 Deciduous trees. 25. 26–29 Classification. 96–97 value of. 47–48. 39. 85–87 Cordaites. 61 Egypt. 89 De Jussieu. 25–26. Gherhards. 29 Club fungi. 84 Evolution algae and. 10–11. 76 Cladistics. 20 China. 109–111 of bryophytes. 13 Chlorophytes. 77 Coal. 70 of cycadeoids. 103–104 of bryophytes. 20. ancient. 64 Cone scales. 84. 20 Endosperm. 39. 29 Dicots. 82. 109 Ephedras. 72 Crutose lichens. 37. 6 Eudicots. 101 Ebers papyrus. 101. 88. 92 Cycads (Cycadophyta). Charles. 109. 25 De Materia Medica (The Material of Medicine. 29. 41 Chi'en Nung (emperor of ancient China). 40. 57 classification and. 110 Eukaryotic organisms. 22 Clades of angiosperms. 6 Doctrine of Signatures. 35 Chlorophylls. 20 Ecological systems algae and. 60–61 . 13 Chytrids. 23 Diversity of angiosperms. Tang Shen-wei). 20 Chitin. 52 130 Cyanobacteria. 109 Equisetales. 80 Conifers. 107. 85 of Welwitschia mirabilis. 96 Dawn redwoods. 92 of cycads. 70–71 Ethnobotany. 37. 91 of gymnosperms. 43 functioning of. 87. 23. 36. 12 Evergreens. 111 Energy conversion. 27 of seedless vascular plants. 57 Double fertilization. 45. 92 Darwin. 42–43 Club mosses. 101–104 Dikaryotic cells. 82 of pines. 64. 84 Decomposers. 34. 20 Chestnut blight. 89 of gnetophytes. 46. 27 Dichotomous keys. ancient. 52 of angiosperms. 70 Cotyledons. 69–70. 92 Core angiosperms. Antoine Laurent. 6 succession of. 44 decomposers and. 104–105. 102–104 Corms. 40 Cibo. 26.
66 Genus names. 76 of seeds and pollen. 76 Fiddleheads. 91–92 heterospory and. 80–81 value of. 34. 67–68 described. 109. 54. 105 Flagella. 40–41 Gnetophytes. 34. 42–43 evolution of. 43 Herbal medicines. 29 Flowering plants. 87–89. 91 Granite mosses. 66. 92 Glomeromycota. 39. 69 of seedless vascular plants. 77 Four-merous flowers. 66. 76 Five-merous flowers. 39. 49 Fuchs. 93 Hallucinogens. 87. 6. 93 seedless vascular plants as. 82 stomata and. 72. 9. 70–74. 41–42 major groups of. 29. 29. 68 of roots. 25. 66. 40 lichens and. 110–111 fungi as. 57 Herbaria. 56. 77 Field guides. 73. 84 Ginkgos. 64. 40. 21 Fungi anatomy of. 73 Fruits. 36–37. 34. 26 of fungi. 44–46 Gymnosperms evolution of. Luca. 60 ginkgos and. 8. 57. 91 seeds of. 107 Greece. 58 See also phylogeny Fabaceae. 39. 82.cladistics and. 12. 89. 42 gymnosperms as. 105 Fronds. 15. 26–29 Darwinian theory of. 20 Green algae. 105–107. 40 Flavonoids. 22 Herbs. 21–22 Giant rafflesia. 14. 34 angiosperms as. 110–111 Fruticose lichens. 40 geological timescale of plants. 84 of seedless vascular plants. 100 of bryophytes. 82. 107 Heterospory. 47–48 life cycle of. 57 Generations. See angiosperms Foliose lichens. 36. 37. 73–74. 22 Herbarium sheets. Leonart. 88 of gymnosperms. 84–85 major groups of. 84 life cycle of. 35–36 dangers of. 15 of gymnosperms. 10 Ferns. 59 Grasses. 39–43 members of. 45 value of. 68 Heterotrophs. 29 Filicales. 12. 37. 29. 23 Ghini. 10. ancient. 85–89. 54. 67–68 Gemmae. 110 Giant sequoias. 49 Food algae as. 105–106 Families. 42 Gametes. 82. 59. 15. 98 Gametophytes of angiosperms. 36 See also fungi 131 . 12 mutualistic relationship with algae. 34. 46 Floras. 91–92 features of. alternate.
4 of seedless vascular plants. 15 . 7–8. 20 Medicine Doctrine of Signatures and. 89 Kelp. Theophrastus). 70 of ophioglossoid ferns. 68 Meiosis of chytrids. 67–68 Liliaceae. 42 gymnosperms as. 36 Hornworts. 20 Homeopathic medicine. 20 The Materials of Medicine Arranged According to Pattern (Tang Shen-wei). 103–104. 61 Horsetails.Historia Naturalis (Natural History. 71 of seedless vascular plants. 101–102 evolution of. 104–105 Linnaeus. 109 Magnoliids. 22. 108–109 Isotales. 111 of bryophytes. 60–61 Lycophytes. 42 described. 71–72 of monilophytes. 15 of angiosperms. 61 prescription drugs. 58. 80 132 Legumes. 70–71 Hunter-gatherers. 101. 66 of lycophytes. 105–106 Lepidodendron trees. 57 mosses as. 6. 89 herbal. 66. 68 of marattoid ferns. 10 different. 4 Hydroids. 11 Iridaceae. 109–110 Inflorescences. 110 International Botanical Congresses. 44–45 of gymnosperms. 59 Life cycles alternation of generations. 34. 73 Honey mushrooms. 54. Carolus. 98. Engelbert. 73 The Material of Medicine (Dioscorides). 92 Magnol. 57 fungi as. 36–37. 59 Hyphae. Pierre. 64. 100–101. 56. 47–49. 93 Identification guides. 57 Homospory. 23 Magnoliaceae. 68–70. 70 Kaempfer. 69 of water ferns. 8 Leaves cotyledons of angiosperms. 67–68. 40. 82. 67–68 of fungi. 41–42 of green algae. 57. 8–10. 110 Magnoliopsida. 9–10 International Code of Botanical Nomenclature (ICBN). 73 of Welwitschia mirabilis. 84–85 length of. 108. 11–13 Landscaping. 47 Kingdoms definition of. 98–99. 93 "The Language of Flowers. 101–104 Marattoid ferns. 40 of club fungi. 6 Megaphylls. Pliny the Elder). 71–72 Marsileales." 96 Latin. 29 Illiciales. 109 Liliopsida. 59 Lichens. 70 Megaspores. 35–36 Hypotheses. 64 Leptoids. 20 Historia Plantarum (History of Plants. 66. 23 Liverworts.
64. 47 133 . 47 See also photosynthesis Pinaceae. 58 value of. 42–43 Mutualism. 101. 15. 20 Natural selection. 26–29. 47 Phycology. 13 Peat mosses. 107 Natural classification system. 107. 45 of gymnosperms. 13 red algae and. 107 Pollen of angiosperms. 7. 25 Natural History (Pliny the Elder). 70–74. 101. 12 Protista Kingdom. See gymnosperms Norfolk Island pines. 85 Modern classification system. 20 Podocarpaceae. 25 Ornamentation. 87. 59. 6 Printing press. 37. 93 Plantae Kingdom. 93 See also evolution Pigments. 108–109 Ovules of angiosperms. 109 Orchids. 41–42 Mycorrhizae. 22–23 Prantl. 110 Monophyletic groups. 87 Poisons. 12 The Origin of Species (Darwin). 68 Mitosis. 88. role of. 42 Microspores. 104–105. 26 Molds. 6 Phycobilins. 97–98. 100. 35–37. 20–21 Prokaryotic organisms. 11 Organelles. 84–86. 98 Pharmaceutical industry. 93 Nonflowering seed plants. 110–111 evolution of. 76 Monkey puzzle trees. 82. 61 Mushrooms. 46. 12 Protists. 42–43. 104. 87 Monocots. 80 Narcotics. 58–59. 85. 89 Morphology. 31 Phylogeny. 41 Mycorrhizal fungi. 85–86 Pines. 100 of gymnosperms. 101 Orders. See gymnosperms Names/naming. 98. 109–110 Ophioglossoid ferns (ophioglossales). 34. 105. 13 Photosynthesis described. 41. 84 Photoautotrophs. 45. 87. 109 Prasinophytes. 6 Phloem. 42 Petals. 27. 56. 25 Naval stores. 93. 44 Phylocode. 34. 107. 13 Plants. See taxonomy Namib Desert. 47–48 Mycelia of fungi. 91 Polynomial nomenclature. 61 Penicillin.of green algae. 10. 47 sporophytes of hornworts. 69 Naked seed plants. defining traits of. 89 Parasitic plants. 36–37 Nymphaeaceae. 85 Paleobotanists. 45 Prescription drugs. 82 of gymnosperms. 12. 108. 71 Orchidaceae. 13–14 Pliny the Elder. 84–85 of sac fungi. 29 Mosses. 87 Nuclei. 34 Monilophytes.
59 definition of. 45. 57. 54. 69. 40. 34. 57. 64–65. 67. 84 of seedless vascular plants. 110 Species abbreviations for. 57 of gymnosperms. 59 value of. 56 Psilotales. 67. ancient. 105 Roses. 66. 70 Ranunculaceae. 107 . 82 Sepals. 80–81 value of. 40. 91. 91 Protonemas. 101 Red algae. 58. 85. John. 10–11 of fungi. 71. 66. 54. 13 of seedless vascular plants. 68–69. 45 Smuts. 8 in Plantae Kingdom. 69 Sporangia of gymnosperms. 43 Sloths. 29. 47 of angiosperms. 80 Sunflowers. 58 Stoneworts. 100. 86. 70–71 Puffballs. 69. 58. 70 Sporophytes of angiosperms. 59 Sexual reproduction. 37. 68–74. 42 Quillworts. 56. 87. 69 Sterile jackets. 74 Spadixes. 76 features of. 40. 68. 70. 65–66 life cycle of. 46. See life cycles Respiratory illnesses. 39. 22. 23 Sphagnum moss. 89 Resurrection plants. 101 evolution of. 46. 11 of algae. 43 Sori. 73–74 Spores asexual reproduction of. 36. 66. 52. 105 Rusts. 37. 56 Rome. 47 Red tides. 73 Species Plantarum (Linnaeus). 44–45. 61 Spike mosses. 84–85 of seedless vascular plants. 41–42. 101 of bryophytes. 92 Seedless nonvascular plants. 134 56 Shelf fungi. 67–68 major groups of. 73 Seed ferns. 64. 84 of seedless vascular plants. 20 Roots. 41–42 Salviniales. 15 of gymnosperms. 56 Sporophylls. 70–71. 41–42. 44–45. 70 Rosaceae. 56. 69 Rhizoids. 4.Protogymnosperms. 40 of gymnosperms. See Bryophytes Seedless vascular plants evolution of. 96. 43 Sac fungi. 70. 66. 68–69. 76–77 Seeds of angiosperms. 76 with moss in name. 109 of bryophytes. 46 Strobili. 66. 89 identifying name. 47 Redwood trees. 14 Stomata of hornworts. 59 described. 67 sexual reproduction of. 54. 98 Seta. 98. 43 Reproduction. 82. 82 naked. 84 Religious ceremonies. 109 Ray.
70–71 Whorls of flowers. 57 Tang Shen-wei. 31 Tepals. 80. 98 Thallus.Symbiotic relationships. 82. 105 Xylem. 8–10. 34. 76 True mosses. 29. 58 Theophrastus. 73 Welwitschia mirabilis. 98. 31 early. described. 40 135 . 57. 11 levels of. 7–8 common plant names. 7 Doctrine of Signatures and. 11 Taxonomy abbreviations and. 37. 42 Tracheids. 57 Water ferns. 105 Toadstools. 65 Tracheophytes. 65 Vegetative reproduction. 69. 109–110 True ferns. 106 Systematics classification. 31. 22–23. 89 Whisk ferns. 93 phylogeny. 20 Taxa. 10 taxonomy. 73–74. 64. 10 Phylocode system. 105 Tribal peoples. 25 hypotheses in. 39. 26 Three-merous flowers. 7–11. 57 ICBN rules. 6 Trimeniaceae. 20 Theory. 10–11 data used. 59 Vascular plants. 26 Trees. 84 Zygomycetes. 11 binomial system. 84. 65 Tree of Life Project. 40 Zygospores.
Gibson is a member of the Project Kaleidoscope Faculty for the 21st Century in recognition of his efforts to improve undergraduate science education.S.D. He has published a variety of research papers and presented his work at scientific conferences. plant population genetics. plant morphology.J. He is currently an associate professor in the Department of Botany and Microbiology and the Department of Zoology at the University of Oklahoma. and human immunodeficiency virus (HIV). She is currently pursuing a career in children's literature. 136 . She has worked as a scientific illustrator and also as a research assistant studying. He also conducts conservation-focused research on tree species. His research investigates the ecology and evolution of plant reproductive systems. Phil Gibson holds degrees in botany from Oklahoma State University (B.) and the University of Georgia (M. in environmental population and organismic biology from the University of Colorado.S. Gibson holds a bachelor's degree in zoology from the University of Georgia. and a Ph. He is also an active member of the Botanical Society of America and the Association of Southeastern Biologists. terri r.). among other things.