Arachis hypogaea, the peanut or groundnut, is an annual herbaceous plant in the Fabaceae (legume or bean family) that originated and was domesticated in South and Central America 3,500 years ago, and is now grown in tropical and warm-temperate regions worldwide for its seeds and their oil. Although appearing as and referred to as a nut, it is actually the underground pod of a legume, rather than a true nut.
The peanut plant has procumbent (trailing) stems and grows to around 0.5 m (20 in) tall or long. The leaves are alternate and compound, with 4 ovate to oblong leaflets, up to 6 cm long (2.25 in). The tubular, 5-parted flowers are yellow and self-fertile. After pollination, the flower stalks elongate, growing to 6 cm long, and push the developing pods into the ground, so that the fruit must be dug up from the soil to be harvested. The fruit is an indehiscent legume (a pod that does not have sutures or split open freely), typically containing 1 to 3 soft seeds (sometimes as many as 6), each covered with a reddish brown, papery membrane. The seeds contain up to 50% oil. Numerous cultivars have been developed, which have different growth forms, size, shape, flavor, and disease and insect resistance; the varieties are generally classified into four major groups, two upright (Valencia and Spanish), and two with prostrated plants (Virginia and Peruvian).
Peanuts, which are high in protein and vitamin B and E, as well as magnesium, manganese, and phosphorus, are eaten raw or boiled and roasted (and often salted) as a snack, and they are cooked in a wide variety of southeast Asian, African, and South American dishes (ranging from soups, stews, and curries to the peanut sauces typical of Indonesian satay and various Asian noodle dishes), as well as used in confections. They are frequently ground into peanut butter, or pressed for the oil, which is used in cooking, salad dressings, margarine, and mayonnaise, as well as in the manufacture of soaps and cosmetics. The seeds, pods, and whole plants are also a source of animal fodder, fiber for paper production, and a green fertilizer.
Total commercial production of peanuts worldwide was 37.6 million metric tons, harvested from 24.1 million hectares, in 2010. China was the leading producer, harvesting more than 3 times as much as any other nation. Other major producers include India, Nigeria, the U.S., Senegal, and Myanmar. In the U.S., peanuts are an important crop in several southeastern states, partly due to the work of the African-American botanist George Washington Carver, who in the 1920s and 1930s promoted them as an alternative crop to cotton, which was declining in productivity due to soil depletion and insect devastation (by the boll weevil, Anthonomus grandis); he famously described 145 different products made from peanuts, many of which he himself developed.
(Bailey et al. 1976, Flora of China 2010, van Wyk 2005, Wikipedia 2012.)
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