The diploid species einkorn and tetraploid species emmer are early wheat species. Tetraploid forms are larger and coarser than diploid forms. To prevent spawning, sterile oysters are now cultured by crossbreeding tetraploid and diploid oysters. The ploidy level for the species range from diploid (2n), tetraploid (4n), to hexaploid (6n). It can be diploid or tetraploid. The first is the number of chromosomes&colon; whether the plant is diploid, triploid or tetraploid. This is actually a species complex that includes distinct diploid and tetraploid races. "Trifolium repens" is a tetraploid (4n=32) with two diploid ancestors. All species are diploid (n=10) with the exception of "Z. perennis", which is tetraploid (n=20). The first comprises species with tetraploid and hexaploid genomes, with long capsules. Typical allopolyploids are tetraploid or hexaploid, XXYY or XXYYZZ. Botanical authorities have listed it as tetraploid and hexaploid in North America (subsp. This interspecific breeding allowed for the creation of three new species of tetraploid "Brassica". Next to a haploid stage "C. albicans" can also exist in a tetraploid stage. "Eragrostis tef" is a self pollinated tetraploid annual cereal grass.