Buckwheat: is related to sorrel, knotweed, and rhubarb

https://en.wikipedia.org/wiki/Buckwheat
Buckwheat
From Wikipedia, the free encyclopedia

Field of buckwheat in Bumthang (Bhutan)

Buckwheat (Fagopyrum esculentum) is a plant cultivated for its grain-like seeds, and also used as a cover crop. To distinguish it from a related species, Fagopyrum tataricum that is also cultivated as a grain in the Himalayas, primarily in Nepal, Bhutan and India, and from the less commonly cultivated Fagopyrum acutatum, it is also known as Japanese buckwheat[2] and silverhull buckwheat.[2]

Despite the name, buckwheat is not related to wheat, as it is not a grass. Instead, buckwheat is related to sorrel, knotweed, and rhubarb. Because its seeds are eaten and rich in complex carbohydrates, it is referred to as a pseudocereal. The cultivation of buckwheat grain declined sharply in the 20th century with the adoption of nitrogen fertilizer that increased the productivity of other staples.