Buckwheat refers to plants in two genera of the family Polygonaceae: the Eurasian genus Fagopyrum, an the North American genus Eriogonum. The crop plant, common buckwheat, is Fagopyrum esculentum. Tartary buckwheat (F. tataricum Gaertn.) or "bitter buckwheat" is also used as a crop, but it is much less common. Despite the common name and the grain-like use of the crop, buckwheats are not grasses and are not related to wheat. The agricultural weed known as Wild Buckwheat (Fallopia convolvulus) is in the same family, but not closely related to the crop species. Within Fagopyrum, the cultivated species are in the cymosum group, with F. cymosum L. (perennial buckwheat), F. giganteum and F. homotropicum. The wild ancestor of common buckwheat is F. esculentum ssp.ancestrale. F. homotropicum is interfertile with F. esculentum and the wild forms have a common distribution, in Yunnan. The wild ancestor of tartary buckwheat is F. tataricum ssp. potanini.