Peanut

An annual herb 30–50 cm tall. Leaves are opposite and pinnate with four leaflets 1–7 cm long and 1–3 cm broad. The flowers are typical pea flowers, yellow with red veins, on a 2–4 cm stalk. After pollination the flower stalk (gynophore) elongates and pushes down into the soil, where the pod develops — the unusual underground fruiting (geocarpy) of this legume. The pod is 3–7 cm long and holds 1–4 seeds. The species epithet 'hypogaea' means 'under the earth'. The roots bear nodules with nitrogen-fixing bacteria.

The peanut is native to South America, domesticated in the Chaco region (Paraguay, Bolivia) and spread worldwide by the Spanish and Portuguese. It is an important grain legume and oil crop in the tropics and subtropics. The oil-rich seeds are pressed for cooking oil and made into peanut butter; peanut sauces are common in Southeast Asia, West Africa and Latin America; the oilcake is used as animal feed and fertiliser; the tops are used for silage. Peanut oil is also used in industry (paint, varnish, furniture polish). In Vietnam, peanuts are boiled, roasted with salt, made into peanut butter and candy, and pressed for oil. Note: some people are allergic to peanuts, sometimes severely.