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.