There are a great many varities of this species some of which have been considered separate species. Formerly considered in the genus Cassia.
Many ID books and botanical keys mention that the way to differentiate between Chamaecrista fasciculata and the very similar Chamaecrista nictitans is by the presence or absence of a stalk on the gland which is at the base of the leaf petioles. The best way to tell the two species apart is by the flower, which is very different in size between the two species. Vegetatively the two species are practically identical.
The yellow flowers are irregular in shape. Blooms first appear in mid spring and continue into early fall. The lower petal is much larger and more spreading than the others.