Winged bean

Winged bean (Psophocarpus tetragonolobus), also called Goa bean or four-angled bean, is a herbaceous climbing legume of the pea family (Fabaceae), 3–4 m long, climbing by tendrils and able to persist for years through underground tubers. Its leaves are trifoliate with triangular, entire leaflets. The large pale blue-purple pea flowers are borne in the leaf axils. The pod is 15–30 cm long and distinctive for its four serrated wings running lengthwise, containing 8–20 round brown seeds. Notably, the plant produces underground tubers up to 8 cm across that are rich in protein. Almost every part of the plant — leaves, flowers, young pods, ripe seeds and tubers — is edible, making the winged bean a potential food crop. The species is native to Southeast Asia and is widely grown in Vietnam and other tropical countries.

The winged bean is a multipurpose vegetable: young pods are eaten as a vegetable (stir-fried, boiled or in salads), the flowers are eaten fresh, young leaves are cooked in soup, seeds are roasted or cooked, and tubers are boiled like potatoes. The seeds and tubers are rich in protein (about 30–40% in dry seed) and oil, an important source of plant protein. Through root-nodule bacteria it fixes nitrogen and is often used as green manure, cover crop and in rotation to improve soil; the leaves and tubers also feed livestock. The plant prefers a hot, humid tropical climate, grows quickly and needs a trellis; it is propagated by seed or tuber and pods after about 2–4 months. In Vietnam the winged bean is widely grown in the lowlands and midlands for its young pods as a vegetable.