Vigna subterranea

Vigna subterranea, the Bambara groundnut, is an annual herbaceous legume (Fabaceae) growing 25–37 cm tall with creeping stems that radiate at ground level from a short central crown. The trifoliolate leaves bear three oval to lanceolate leaflets, each held on a long petiole, and are subtended by small stipules about 3 mm long. Small yellow pea-like flowers emerge near soil level on short peduncles, with a tube calyx about 1 mm long and a whitish-yellow corolla 4–7 mm long. After fertilisation the peduncle elongates and curves downward, pushing the developing pod into the soil, where it matures geocarpically — a nearly spherical pod about 2.5 cm in diameter containing one or two hard, round, brown to red seeds. Native to West Africa, particularly the region of Nigeria, Cameroon, and the Central African Republic, the species was domesticated there centuries ago and is now widely grown across sub-Saharan Africa as a drought-tolerant pulse crop on poor, sandy soils.