Formerly known as Leguminosae, this is the third largest family of flowering plants on earth. Only Orchidaceae (24,000 species) and Asteraceae (20,000 species) are larger. A wide variety of plant types are included in the 18,000 identified species of legumes from herbs to shrubs to trees. They form pod shaped fruit and have a soil bacteria associated with their roots that fix nitrogen from the air and make it available to the plant.