Peanut, also groundnut or monkey nut, common name for an annual warm-season plant of the legume family, and for its seeds. Peanuts originated in South America, probably in Brazil, and have been cultivated since ancient times by Native Americans. Plants grow about 75 cm (30 in) tall and can spread 1.2 m (4 ft). Some forms of the plant develop a bunchy erect growth; others, called runners, spread over the ground. The peanut is unusual in that, when the flower has been fertilized, the elongated receptacle, called the peg, turns downward from the base of the flower stalk to bury the ovary in the soil, where the pod develops. Usually, two seeds develop in each pod.

There are many types of peanuts, and both large- and small-seeded kinds are grown extensively. Large-seeded varieties are used for roasting and for sweets, and small-seeded types are used for peanut butter and oil. When peanuts have been harvested, the green parts of the plants are used as forage for livestock. The traditional use as fodder and grain feeds for cattle and pigs has declined.

Peanuts require sunshine, a warm growing season of 120 to 140 days, and moderate rainfall. They do best on well-drained sandy soils; dark soils tend to stain the shells.

Peanuts are nutritious and high in energy. The seeds contain 40 to 50 per cent oil and 20 to 30 per cent protein, and they are an excellent source of B vitamins. In India, peanuts are boiled and the resulting liquid strained to produce groundnut milk. Peanut oil is also popular as a high-quality salad and cooking oil, and is commonly used in margarine.

The leading peanut-producing countries, in order of production, are China, India, and the United States. In the United States peanuts are grown primarily for food; in other countries they are used principally for edible oil.

Scientific classification: The peanut belongs to the family Fabaceae (or Leguminosae); it is classified as Arachis hypogaea.

Reviewed by: Department of Botany, Natural History Museum