Buckwheat refers to plants in two genera of the dicot 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 therefore considered pseudocereals) and are not related to wheat nor other monocots. 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.
The fruit is an achene, similar to sunflower seed, with a single seed inside a hard outer hull. The starchy endosperm is white and makes up most or all of buckwheat flour. The seed coat is green or tan, which darkens buckwheat flour. The hull is dark brown or black, and some may be included in buckwheat flour as dark specks. The dark flour is known (exaggeratedly) as "blé noir" ("black wheat") in French, along with the name sarrazin ("saracen").
Buckwheat noodles play a major role in the cuisines of Japan (soba), Korea (naengmyeon, makguksu and memil guksu) and the Valtellina region of Northern Italy (pizzoccheri). Soba noodles are the subject of deep cultural importance in Japan. In Korea, before wheat flour being replaced for making guksu, the generic term referring to noodles, buckwheat noodles were widely eaten as hot dishes. The difficulty of making noodles from flour that has no gluten has resulted in a traditional art developed around their hand manufacture.
Buckwheat groats are commonly used in western Asia and eastern Europe. The porridge was common, and is often considered the definitive peasant dish. It is made from roasted groats that are cooked with broth to a texture similar to rice or bulgur. The dish was brought to America by Russian and Polish Jewish immigrants who called it "kasha" and used it mixed with pasta or as a filling for knishes and blintzes, and hence buckwheat groats are most commonly called kasha in America. Groats were the most widely used form of buckwheat worldwide during the 20th century, with consumption primarily in Russia, Ukraine and Poland.
Buckwheat pancakes, sometimes raised with yeast, are eaten in several countries. They are known as buckwheat blinis in Russia, galettes in France (savoury crêpes which are especially associated with Brittany), ployes in Acadia and boûketes (that is, named the same as the plant they are made of) in Wallonia. Similar pancakes were a common food in American pioneer days. They are light and foamy. The buckwheat flour gives them an earthy, mildly mushroom-like taste. In Ukraine, yeast rolls called hrechanyky are made from buckwheat.
Farina made from groats are used for breakfast food, porridge, and thickening materials in soups, gravies, and dressings. In Korea, buckwheat starch is used to make a jelly called memilmuk. It is also used with wheat, maize or rice in bread and pasta products.
Buckwheat contains no gluten, and can thus be eaten by people with coeliac disease or gluten allergies. Many bread-like preparations have been developed.
Besides the seeds, from which buckwheat flour is produced, buckwheat is also a good honey plant, producing a dark, strong monofloral honey.
Buckwheat greens can be eaten. However, if consumed in sufficient quantities, the greens, or, more commonly, their juice, can induce sensitization of the skin to sunlight known as fagopyrism. Fair skinned people are particularly susceptible, as are light pigmented livestock. Enthusiasts of sprouting, however, eat the very young buckwheat sprouts (four to five days of growth) for their subtle, nutty flavour and high nutritional value. They are widely available in Japan.