Middle states south-ward and west to the Rockies.
Flowers: large; growing on slender axillary flower-stalks. Calyx: of five almost separate petals. Corolla: one and a half inches broad; of five petals; four of which are nearly equal and two dotted with purple at the base; the fifth one being larger. Stamens . ten; anthers, irregular, of which some are laden with a yellow, others with a purple, pollen. Pistil: one. Pod: flat. Leaves: pinnate; divided into ten to twenty pairs of small, linear, sensitive leaflets which close when roughly handled, the lowest pair possessing a club-shaped gland at the base.
When looking at the illustration it would appear as though the wild senna and the partridge pea had, to amuse themselves, played at exchanging their leaves, for the eye naturally associates the larger leaves with the larger flowers. Just the reverse, however, is true, and the strength that has been reserved in the small leaves of the partridge pea, bursts forth in the large bright flowers which enliven many a sandy bank in late summer. It is especially in the south that its bloom is most perfect. The sensitiveness of these plants to the touch is a curious feature.