Common bean

An annual herb, either a low bush 30–60 cm tall or a climbing twining vine 2–3 m long over supports; stems finely hairy. The leaves are compound with three ovate-lanceolate entire leaflets plus small stipules. The typical butterfly (papilionoid) flowers of the legume family are white, pink or purple, in axillary clusters, self-pollinating. The pods are 10–20 cm long, slightly curved and hang down; immature pods are green, yellow or purple and are eaten whole with the young seeds; old pods dry and split and twist open. The seeds are flattened kidney-shaped, 0.5–1.5 cm, in a huge range of colours — white, cream, yellow, red, black, brown and mottled — with 20–25% protein. Raw seeds contain phytohaemagglutinin (a red-cell agglutinating toxin) destroyed by boiling for about 30 minutes.

The common bean was domesticated in the Americas about 8,000 years ago, independently in two regions — Mexico–Central America (bush types) and the Andes (climbing types) — spread to Europe after Columbus and became a staple protein of the Old World, later carried worldwide. Today thousands of cultivars exist in many colours, sizes and growth habits. In 2022 about 28 million tonnes of dry beans were produced, led by India with about 23%; Brazil, Mexico, China and Tanzania are also large producers; counting fresh green beans, China and Indonesia lead. In Vietnam, common beans are grown widely in Đà Lạt–Lâm Đồng (quality climbing types), the Mekong Delta and peri-urban farms; young pods are stir-fried, boiled or braised and dry seeds go into sweet soups and glutinous rice. Bean roots fix nitrogen with Rhizobium bacteria, making them excellent in rotation.