Legumes are members of the third largest family (Leguminosae) of flowering plants, and are globally distributed, with as many as 19,000 species. Several species have the ability to undergo a symbiotic association with nitrogen-fixing bacteria of the genera Rhizobium or Bradyrhizobium. Consequently, legumes tend to have high protein contents, and are an essential source of food, feed, and forage. They are also used as ornamentals, or valued for green manure, timber, gums, and other compounds.