Other plants found include ferns, horsetails, club mosses, and conifers. Ginkgo trees, conifers, bennettites, horsetails, ferns and cycads were plentiful during this period. Vascular plants include the clubmosses, horsetails, ferns, gymnosperms (including conifers) and angiosperms (flowering plants). Extensive swamps developed with mosses, ferns, horsetails and calamites. On land, North America's vegetation included plants like conifers, cycads, ferns, ginkgoes, and horsetails. There were also ginkgos, czekanowskialeans, bennettitaleans, ephedra, horsetails, ferns, and mosses. It may have eaten ferns, cycadeoids, seed ferns, horsetails, and algae. The presence of ferns, cycads, and horsetails indicates a generally humid climate. By the Middle Devonian, shrub-like forests of primitive plants existed&colon; lycophytes, horsetails, ferns, and progymnosperm. Vegetation consisted of ferns ("Cladophlebis"), horsetails, and giant conifers ("Protojuniperoxylon"). The fern allies are represented by 44 native species of psilophytes, horsetails and lycophytes. The leaves of horsetails are arranged in whorls fused into nodal sheaths. Twinflower, strawberries, bunchberries, horsetails and wintergreen form an attractive grown cover. Calamitaceae is an extinct family of plants related to the modern horsetails. Rhizomes generally form a single layer, but in giant horsetails, can be multi-tiered.