Vigna unguiculata (L.) Walp.

Herbaceous annual or perennial, erect, trailing or twining, cultivated or wild, chiefly in grassland, but also in open woodland and woodland edges. Root system shallow, adventitious or turbinate tubers, nodules common on all systems. Stems variable in thickness, patent, pubescent to aculeate, scabrid to glabrous, hairs colourless. Leaflets variously shaped, from obtusely trilobed to more or less triangular-rhomboid to elongate-hastate, texture variable from soft chartaceous to coriaceous, pubescence variable from strigose on both lamina surfaces to sparsely strigose on dorsal nerves only. Stipules typically spurred, i.e. appendaged below the point of attachment; variable from large, broadly ovate and most obvious, green, extremely strigose and ranging to hairy on ribs only or glabrous, to relatively small, lanceolate, brown and glabrous, all margins ciliate. Inflorescence axillary, a raceme varying from elongated with 4-7 flowers to contracted with 2 flowers, extrafloral nectaries alternating with flowers. Flowers blue, mauve, purple to pinkish mauve. Calyx campanulate, lobes longer or shorter than tube, variably strigose, the two upper lobes connate up to half their length, rugose and plicate with age. Standard known to snap closed from the time of anthesis to a few hours later, buff or yellowish on outer surface so that the closed flower appears to be yellow as reported by many collectors, oblate, upper pair of calluses narrow, perpendicular, more or less parallel or divergent. Keel straight, obtuse, slightly canoe-shaped, paler mauve to white, contains no pockets. Stamens 9, connate to form an open tube in the lower part, free filaments of two lengths, anthers entangled with dorsal style brush so that they distribute pollen when forced through the rigid keel opening as it is suppressed by visiting insects, vexillary stamen free, geniculate at base. Nectary collar-shaped, lobed, surrounding base of ovary. Ovary pilose to pubescent or puberulous with long stiff hairs along the suture. Style elongation extended horizontally or up to an angle of ca. 45° beyond the stigma, flattened, rounded or truncate, 0.2-0.8(-1.0) mm long, the whole appearing hammer-shaped. Legumes erect or pendant, black to yellow, varyingly pubescent to glabrous, from ca. 200-300 mm in cultivated forms (900 mm in cv. gr. sesquipedalis) and ca. 60-100 mm long in the wild forms, beaked, twisted spirally for seed dispersal in wild forms, non-dehiscent in cultivated forms. Seeds variable in colour from white, red, light to dark brown or black, often mottled, size variable from 6-9 mm in cultivated forms, much smaller in wild forms, hilum eccentric, aril ring-like.

It grows in tropical and subtropical climates. It grows from sea level to 1800 metres altitude in the tropics. In Ethiopia it grows between 500-2,000 m above sea level. Plants can stand high temperatures. Some kinds can tolerate drought. They are sensitive to cold and killed by frost. Plants germinate with a temperature between 11.5-15.5°C. The best growth is between 20-35°C. They can grow on a range of soils providing they are well drained. They are a short day plant. They do well in the semiarid tropics. It will not tolerate acid or alkaline soils. It grows in areas with an annual rainfall between 280-410 mm. It can grow in arid places. It can tolerate shade so is good for inter-cropping.

The young leaves, young pods and ripe seeds are all eaten. They can be steamed, boiled, stir-fried etc. The leaves can be dried and stored. The dried seeds are used in soups and stews. They are ground into flour or fermented. The seeds are also used for bean sprouts. Roasted seeds are used as a coffee substitute.

It is grown from seeds. Seed collection is easy. Seeds remain viable for several years if carefully stored. A seeding rate of about 20 kg per ha is suitable and seed are sometimes broadcast then thinned. Cowpeas mostly inbreed giving pure lines.