A very large family, including many important plants, such as Clover, Alfalfa, Peas, and Beans; herbs, shrubs, vines, and trees, distinguished principally by the flower and fruit, resembling the butterfly-like corolla and simple pod of the common Pea; leaves alternate, usually compound, with leaflets and stipules; calyx five-toothed or five-cleft; petals five. The upper petal, or "standard," large, covering the others in the bud, the two at the sides standing out like "wings," the two lower ones united by their edges to form a "keel," enclosing the stamens, usually ten, and the single pistil with a curved style; the ovary superior.

There are numerous kinds of Anisolotus, widely distributed, common, difficult to distinguish; mostly herbs, some slightly shrubby; leaves with two or many, toothless leaflets; calyx-teeth nearly equal; petals with claws, free from the stamens, wings adhering to the keel, incurved, blunt or beaked; stamens joined by their filaments, in two sets of one and nine, anthers all alike; style incurved; pods two-valved, often compressed between the seeds, never inflated. These plants have several common names, such as Bird-foot, Trefoil, Cat's-clover, etc., and are called Crowtoes by Milton.