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Buckwheat refers to plants in two genera of the family Polygonaceae, the Eurasian genus Fagopyrum, and 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 Yunan. The wild ancestor of tartary buckwheat is "F. tataricum ssp. potanini.
The name “buckwheat” or “beech wheat” comes from its triangular seeds, which resemble the much larger seeds of the beech nut from the beech tree, and the fact that it is used like wheat. The etymology of the word is explained as partial translation of Middle Dutch boecweite : boek, beech; see PIE bhago- + weite, wheat.
Common buckwheat was domesticated and first cultivated in southeast Asia, possibly around 6000 BC, and from there spread to Europe and to Central Asia and Tibet. Domestication most likely took place in the western Yunnan region of China. Buckwheat is documented in Europe in the Balkans by at least the Middle Neolithic (circa 4000 BC) and the oldest known remains in China so far date to circa 2600 BC, and buckwheat pollen has been found in Japan from as early as 4000 BC. It is the world’s highest elevation domesticate, being cultivated in Yunnan on the edge of the Tibetan Plateau or on the Plateau itself. Buckwheat was one of the earliest crops introduced by Europeans to North America. Dispersal around the globe was complete by 2006, when a variety developed in Canada was widely planted in China.
Buckwheat is a short season crop that does well on low-fertility or acidic soils, but the soil must be well drained. Too much fertilizer, especially nitrogen, will reduce yields. In hot climates, it can only be grown by sowing late in the season, so that it will bloom in cooler weather. The presence of pollinators greatly increases the yield. The nectar from buckwheat flower makes a dark colored honey. Buckwheat is sometimes used as a green manure, as a plant for erosion control, or as wildlife cover and feed.
Common buckwheat is by far the most important buckwheat species, economically, accounting for over 90% of the world’s buckwheat production. A century ago, Russia was the world leader in buckwheat production. Growing areas in the Russian Empire were estimated at 2,600,000 hectares, followed by those of France (355,000 hectares). In 1970 the Soviet Union grew an estimated 4.5 million acres (18,000 km²) of buckwheat, but has since been overtaken by China. Japan, Poland, Canada, Brazil, South Africa, and Australia also grow significant quantities of buckwheat.
In the northeastern United States, buckwheat was a common crop in the 18th and 19th centuries. Cultivation declined sharply in the 20th century due the use of nitrogen fertilizer, to which maize and wheat respond strongly. Over a million acres (4,000 km²) were harvested in the United States in 1918. By 1954 that had declined to 150,000 acres (600 km²), and by 1964, the last year that production statistics were gathered, only 50,000 acres (200 km²) were grown.