Members of the legume family, the "Fabaceae" or "Leguminosae," fill critical niches in most terrestrial biomes. This is one of the few plant families whose species are capable of "fixing" nitrogen from the air, through association with specialized soil bacteria, for use as a natural fertilizer.
The family has traditionally been divided into three subfamilies. The Caesalpinioideae, consisting of several early-diverging groups, includes species such as brazilwood, carob, honey locust, Kentucky coffee tree, senna and tamarind. The Mimosoideae, recognizable by the distinctive "pom-pom"-like flowers with many anthers and reduced petals, includes species such as acacia, cojoba, mesquite, and mimosa. The Papilionoideae, which contains most of the major crop and forage legumes, includes species such as alfalfa, birds-foot trefoil, chickpea, clovers, cowpea, common bean, fava bean, fenugreek, guar, indigo, jicama, lentil, licorice, lima bean, lupine, mung bean, pea, peanut, pigeon pea, rooibos, and soybean.