peanut, (Arachis hypogaea), also called groundnut, earthnut, or goober, legume of the pea family (Fabaceae), grown for its edible seeds. Native to tropical South America, the peanut was at an early time introduced to the Old World tropics. The seeds are a nutritionally dense food, rich in protein and fat. Despite its several common names, the peanut is not a true nut. As with other legumes, the plant adds nitrogen to the soil by means of nitrogen-fixing bacteria and is thus particularly valuable as a soil-enriching crop.

The peanut is an annual and can either be an erect shrubby plant, 45–60 cm (18–24 inches) high with short branches, or have a spreading form, 30–45 cm (12–18 inches) high with long branches that lie close to the soil. The stems are sturdy and hairy and bear pinnately compound leaves with two pairs of leaflets. The flowers are borne in the axils of the leaves and feature golden-yellow petals about 10 mm (0.4 inch) across. The oblong pods have rounded ends and are most commonly 25–50 mm (1–2 inches) long with two or three seeds; the pods are contracted between the seeds and have a thin, netted, spongy shell. The seeds vary from oblong to nearly round and have a papery seed coat that ranges in colour from whitish to dark purple.