Fabaceae

Legumes
Scientific classification
Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Fabales Family: Fabaceae
Subfamilies
Faboideae Caesalpinioideae Mimosoideae
References
GRIN-CA 2002-09-01

The Family Fabaceae (or Leguminosae) is a family of plants in the order Fabales, and one of the largest families of flowering plants with 650 genera and over 18.000 species. These plants are commonly caled legumes and the group contains some of our most valuable food crops, such as beans, peas, peanuts, soybeans, and lentils. Other members of the family include important plants used for animal feed or green manure such as lupins, clover, alfalfa, and soybean. Some species such as Acacia, Mimosa and Flamboyant are (tropical) ornamental trees. Still other members of the family have medicinal or insecticidal properties (for instance derris) or yield important substances like gum arabic, tannin, dyes, or resins. Finally, kudzu, originally planted for soil improvement and as cattle feed, is a notorious weed that (in the southern U.S. at least) grows over everything.

All members of this family have five-petaled flowers in which the superior ovary ripens to form a pod whose two sides split apart, releasing the seeds which are attached to one seam, alternately attached to one side or the other. They are classified into three subfamilies, sometimes raised to the rank of family in the order Fabales, on the basis of petal shape:

• Faboideae (Fabaceae), also called Papilionoideae: One petal is large and has a crease in it, the two adjacent petals are on the sides, and the two bottom petals are joined together at the bottom, forming a boatlike structure.
• Caesalpinioideae (Caesalpiniaceae): The five petals are equal in size and large.
• Mimosoideae (Mimosaceae): The petals are tiny, and the stamens are the showy part of the flower.

Nitrogen fixation

Many of the members of the legume family have the ability to fix nitrogen from the atmosphere, enabling them (or other plants that grow in the same soil later) to use the nitrogen. This is done by symbiotic nitrogen-fixing rhizobium bacteria which colonise the roots of the plants, forming "root nodules".