is the second largest US family of plants, with 477 genera and around 2,860 species. Common names are pea, or bean family, on account of the seeds, which are small and spherical, contained within an elongated pod; the fruits of many species are edible. Leaves are usually alternate, and compound, either palmate or pinnate.
The majority have bilaterally symmetric flowers, similar in structure; a calyx formed of five sepals - fused at the base, open at the tips - and a flowerhead with five petals, of which one (the banner) is broad and orientated upwards, two (the wings) project at the side, and the other two (the keel) point downwards and are joined along their lower edge. Within the keel, mostly or completely hidden, are (usually) ten stamens, nine of which are fused. A few genera have different flowers, such as senna, where all five petals are similar in shape.