Article # 393. Legume

A legume is a plant in the family Fabaceae (or Leguminosae), or a fruit of these plants. A legume fruit is a simple dry fruit that develops from a simple carpel and usually dehisces (opens along a seam) on two sides. A common name for this type of fruit is a "pod", although pod is also applied to a few other fruit types. Well-known legumes include alfalfa, clover, peas, beans, lentils, lupins, and peanuts. A peanut is not a nut in the botanical sense; a peanut is an indehiscent legume, that is, one whose pod does not split open on its own. The history of legumes is tied in closely with that of human civilization, appearing early in Asia, the Americas (the common bean, several varieties), and Europe (broad beans) by 6,000 BC, where they became a staple, essential for supplementing protein where there was not enough meat.

Legume plants are noteworthy for their ability to fix atmospheric nitrogen, an accomplishment attributable to a symbiotic relationship with certain bacteria known as rhizobia found in root nodules of these plants. The ability to form this symbiosis reduces fertilizer costs for farmers and gardeners who grow legumes, and means that legumes can be used in a crop rotation to replenish soil that has been depleted of nitrogen.

Legume seed and foliage have a comparatively higher protein content than non-legume material, probably due to the additional nitrogen that legumes receive through nitrogen-fixation symbiosis. This high protein content makes them desirable crops in agriculture.

Farmed legumes can belong to numerous classes including forage, grain, blooms, pharmaceutical/industrial, fallow/green manure, and timber species, with most commercially farmed species filling two or more roles simultaneously.

• Forage legumes are of two broad types. Some, like alfalfa, clover, vetch, stylo, or Arachis, are sown in pasture and grazed by livestock. Other forage legumes such as Leucaena or Albizia are woody shrub or tree species that are either broken down by livestock or regularly cut by humans to provide stock feed.

• Grain legumes are cultivated for their seeds, and are also called pulses. The seeds are used for human and animal consumption or for the production of oils for industrial uses. Grain legumes include beans, lentils, lupins, peas, and peanuts.

• Bloom legume species include species such as lupin, which are farmed commercially for their blooms as well as being popular in gardens worldwide.

• Industrial farmed legumes include Indigofera and Acacia species, which are cultivated for dye and food gum production respectively.

• Fallow/green manure legume species are cultivated to be tilled back into the soil in order exploit the high nitrogen levels found in most legumes. Numerous legumes are farmed for this purpose including Leucaena, Cyamopsis, and Sesbania species.

• Various legume species are farmed for timber production worldwide including numerous Acacia species, Erythroxylum species and Castanospermum australe.

The term is derived from the Latin word legumen (with the same meaning as the English term), which is in turn believed to come from the verb legere "to gather." English borrowed the term from the French "légume," which, however, has a wider meaning in the modern language and refers to any kind of vegetable; the English word legume being translated in French by the word légumineuse.

Legumes are good sources of iron and fiber.