IUCN threat status:

Endangered (EN)

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Phaseolus lunatus, butter bean or lima bean, is an herbaceous plant in the Fabaceae (legume or bean family) native to Central and South America, now cultivated in warm, semi-tropical regions throughout the world for its beans, which can be eaten fresh (generally without the bean pods) or dried (although they must be cooked for at least 10 minutes, or treated by fermentation, to destroy toxic cyanogenic glycosides).

P. lunatus includes a large-seeded type, the butter bean, thought to have been domesticated in Peru around 4,000 years ago—hence the common name, lima bean, for the capital of Peru, although the latter name may also refer to the beans from the species P. limensis (which is sometimes classified as a variety of P. lunatus)—and imported to Africa and Madagascar by way of Brazil, A second, smaller-seeded variety, the sieva, was developed later, probably in Central America and Mexico around 500 years ago, and introduced from there to the Philippines and other parts of Asia by the Spaniards.

Plants of both varieties are perennial, but are generally grown as annuals, and have erect bush forms, which grow to around 1 m (3.25 ft) tall, and twining forms, up to 4 m (13 ft) long. Plants have trifoliate compound leaves with oval leaflets, each up to 9 cm (3.5 in) long. The white to yellow flowers, which occur in loose, open unbranched clusters (racemes) develop into broad, flat pods up to 9 cm long. This species requires a long, warm growing season for beans to develop.

Butter beans, which are high in protein, vitamins B and C, and various minerals (including iron, magnesium, phosphorus, and potassium) are sometimes picked when green, shelled, and prepared as a cooked vegetable with a relatively short cooking time (or frozen or canned). More often, however, the beans are harvested when the pods have fully matured and dried. The dried beans are then soaked and cooked for several hours, and cooked into numerous soups, stews, and meat dishes. Dried beans, including this species, are an important source of protein in many parts of Africa, southeast Asia, and South America.

The U.N. Food and Agricultural Organization estimates that total commercial production of dried beans (which includes butter beans but also beans of other species and numerous varieties) was 23.23 million metric tons worldwide in 2010, harvested from 29.92 million hectares. India was the leading producer, responsible for 21% of total production, followed by Brazil, Myanmar, China, the U.S., and Mexico. Within the U.S., the major dried-bean producing states in 2007 were North Dakota, Michigan, Nebraska, Minnesota, and Idaho, although California produces a large share of lima beans.

(Bailey et al. 1976, USDA 2012, van Wyk 2005.)


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