Buckwheat (Fagopyrum esculentum) is a plant cultivated for its grain-like seeds, and also used as a cover crop. Despite the name, buckwheat is not related to wheat, as it is not a grass; instead, buckwheat is related to sorrel, knotweed, and rhubarb. The cultivation of buckwheat grain declined sharply in the 20th century with the adoption of nitrogen fertilizer that increased the productivity of other staples.