Herbs, shrubs and small trees. Leaves spirally arranged; extrafloral nectaries present or not. Inflorescences racemose, axillary and/or terminal; bracteoles absent. Sepals 5. Petals 5, subequal. Seeds and funicle variable.
Americas: present Pantropic: present
A pantropic genus with c. 260 species, c. 1/5 of these in the warmer parts of the Americas. 17 species are treated here, 3 of them indigenous (see note 1 below).
For details on synonymy, literature and typification of the genera Cassia, Chamaecrista and Senna, the reader is referred to the comprehensive revisions by De Wit and . See the note under Cassia (p. 556) for the reasons to recognize Senna and Chamaecrista as genera separate from Cassia. In our area probably only 3 species are indigenous: Senna divaricata, S. timoriensis and S. tora. It is doubtful whether S. siamea is indigenous and the remaining 14 species have all been introduced. Some of them are probably only occasionally met with outside gardens. There are others which we have decided not to include in the key as they have never had any larger distribution as garden plants and are hardly found in any natural vegetation type. A number of taxa, occasionally recorded as in cultivation in Malesia have not been included. See the list on page 690.