Taxonomic and functional implications of stigma morphology in species of Cassia, Chamaecrista, and Senna (Leguminosae: Caesalpinioideae)

Two stigma forms occur in Chamaecrista and Senna, but only one in Cassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.