Phaseolus vulgaris, also known as the common bean is an annual plant grown worldwide for its edible dry seeds or unripe fruit (both commonly called beans). The main categories of common beans, on the basis of use, are dry beans (seeds harvested at complete maturity), snap beans (tender pods harvested before the seed development phase) and shell (shelled) beans (seeds harvested at physiological maturity). Its leaf is also occasionally used as a vegetable and the straw is used as fodder. It is a member of the legume family Fabaceae. Like most members of this family, common beans acquire the nitrogen they require through an association with nitrogen-fixing bacteria, rhizobia.