The term legume has two related meanings in botany:

  1. The common name for plant species in the Family Fabaceae
  2. The name of a type of fruit, characteristic of legumes.
  • A legume is a simple dry fruit that develops from a simple pistil and usually dehisces (opening along a seam) on two sides. Another name for this type of fruit is a pod, although pod is also applied to a few other fruit types. Well-known plants that have legume fruits include Alfalfa, clovers, peas, beans, and peanuts. A peanut is an indehiscent legume — that is, it does not split open along a seam. A peanut is not a nut in the botanical use of the word.

Another characteristic of legumes is that they host bacteria in and on their roots. These bacteria, Rizobium, have the ability to take nitrogen gas, N2, out of the air and convert it to a form of nitrogen that is usable by the host plant, NO3. The legume, acting as a host, and the Rizobium bacteria, acting as a provider of usable nitrogen, form a symbiotic relationship.