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A legume is a plant in the family Fabaceae (or Leguminosae), or a fruit of these specific 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, such as vanilla. Well-known legumes include alfalfa, clover, peas, beans, lentils, lupins, mesquite, carob, and peanuts.

History

The term legume 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.

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.

Fixation of nitrogen in the soil

Legume plants are noteworthy for their ability to fix atmospheric nitrogen, thanks 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 allows legumes to 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.

Uses by humans

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Farmed legumes can belong to many agricultural classes, including forage, grain, blooms, pharmaceutical/industrial, fallow/green manure, and timber species. Most commercially farmed species fill 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.