Stems. - Spreading, eight inches to a foot long. Leaves. - Divided into from ten to fifteen pairs of narrow delicate leaflets, which close at night and are somewhat sensitive to the touch. Flowers. - Yellow, rather large and showy, on slender stalks beneath the spreading leaves; not papilionaceous. Calyx. - Of five sepals. Corolla. - Of five rounded, spreading, somewhat unequal petals, two or three of which are usually spotted at the base with red or purple. Stamens. - Ten, unequal, dissimilar. Pistil. - One, with a slender style. Pod. - Flat.
The partridge-pea is closely related to the wild senna, and a pretty, delicate plant it is, with graceful foliage, and flowers in late summer which surprise us with their size, abounding in gravelly, sandy places where little else will flourish, brightening the railway embankments and the road's edge. It is at home all over the country south of Massachusetts and east of the Rocky Mountains, but it grows with a greater vigor and luxuriance in the south than elsewhere. The leaves can hardly be called sensitive to the touch, yet when a branch is snapped from the parent-stem or is much handled, the delicate leaflets will droop and fold, displaying their curious mechanism.