A climbing leguminous vine grown for both its edible seeds and elongated, sweet-potato-like tubers.
The African yam bean (Sphenostylis stenocarpa, family Fabaceae) is a perennial climber with twining stems 1 to 3 metres long from a tuberous rootstock, scrambling over the ground and into surrounding plants. It is gathered from the wild and also cultivated, an important food crop in Africa with high potential elsewhere: in many parts of tropical Africa it is a staple grown above all for its edible tubers, and also for its leaves, seeds and pods. It fixes nitrogen through bacteria in its root nodules, so the roots are best left in the ground after harvest.
It grows from Guinea to Ethiopia and south to Angola, Zimbabwe and Mozambique, in miombo woodland, bushland by rivers and lakes, grassland and roadsides, often on rocky ground and termite mounds, up to 1,500 metres and occasionally 2,000 metres. It does best at 23 to 29°C with 1,000 to 1,200 mm of rain a year, and it needs a dry period while flowering. It prefers full sun and fertile sandy soil. Although perennial, it is usually grown as an annual: pods can be picked from about five months after sowing for another two months, and the tubers mature at seven to eight months. Good yields are about 2 tonnes of seed and 4 tonnes of tubers per hectare. It is grown from seed or by dividing the tubers.
Source: Useful Tropical Plants database (Fern, K.).
Seeds and tubers are cooked as a protein-rich food; immature pods are also eaten as a vegetable.
Grown as a minor crop, often intercropped with yam and cassava; needs a long growing season and produces long, tough seed pods.