The Polygonaceae or buckwheat family takes its name from Greek poly, "many," and gonu, "knee," referring to the many swollen node joints that some species have. The family includes about 45 genera and some 1100 species. Just three genera, Eriogonum, Polygonum and Rumex, together account for 650 species. The majority of members are perennial herbs. The leaves are simple, almost always alternate, and usually stipulate, and the flowers are small and radially symmetrical with two undifferentiated whorls of 3-6 distinct or basally connate tepals. The fruits are usually 3-angled achenes. The crop species of buckwheat is the Eurasian genus Fagopyrum, while in North America the genus Eriogonum is referred to as wild buckwheat. Despite the name and  the grain-like use of buckwheat, it is not a grass and is not related to the grasses. Many species are weedy invasives.