Sphenostylis stenocarpa aka Yam Pea

Sphenostylis stenocarpa, or African yam bean, belongs to the pea family, Fabaceae. This climbing perennial comes from tropical Africa. Its range spans Guinea to Ethiopia, reaching south to Angola, Zimbabwe and Mozambique. It grows in woodland, grassland and bush beside lakes and rivers. It also occurs along roads, on rocky ground and on termite mounds. People gather wild plants and grow it as a food crop.

The plant grows fast from a tuberous rootstock. Garden descriptions give a height of about 6.6 feet [2 metres]. Twining stems can reach 9.8 feet [3 metres] long. Its listed spread is about 1 foot [0.3 metres]. Stems trail across the soil or climb nearby plants for support. Each leaf has three leaflets. Flowers grow at the leaf axils and may be pink, purple or greenish white. The smooth, flat pods reach about 0.8 feet [0.25 metres] long.

This tropical crop needs full sun and moist, well-drained soil. It grows best in fertile, sandy ground but also accepts loam. It prefers acid soil, with a pH of 5.5–6. Its wider reported tolerance runs from pH 4.5 to 7. Best growth occurs with daytime temperatures of 23–29°C. The reported tolerance spans 15–35°C. It favours annual rainfall of 1,000–1,200 millimetres. A dry spell during flowering is important. PFAF lists USDA hardiness zones 10–12. Growers often treat this perennial as an annual.

Its main garden value lies in food production. People cook young pods and leaves as vegetables. They boil the protein-rich seeds or add them to soups. The white roots also contain protein. People eat them raw or cook them like potatoes. Pod harvest can start about five months after sowing. Picking may then continue for two more months. Tubers mature seven to eight months after sowing. Plants can grow from seed sown in place or from divided tubers.

Root nodules house bacteria that fix nitrogen from the air. This gives the crop a role in soil nitrogen management. PFAF also includes it among plants for food forests. The supplied sources report no known hazards or medicinal uses. They do not provide specific pest or disease information. Their lack of reported hazards does not establish safety for pets.