Buckwheat is a variety of plants in the dicot family Polygonaceae: the Eurasian genus Fagopyrum, the North American genus Eriogonum, and the Northern Hemisphere genus Fallopia. Either of the latter two may be referred to as "wild buckwheat." Despite the name, buckwheats are not related to wheat, as they are not cereals / grasses (family Poaceae); instead, buckwheat is related to sorrels, knotweeds, and rhubarb.

The cultivation of buckwheat grain, a pseudocereal food crop, declined sharply in the 20th century in affluent regions where the usage of nitrogen fertilizer is popular.