The present study is a taxonomic revision and a contribution to establish monographs on a medicinally important genus, Cassia L. sensu lato, in the Sudan, so as to help in standardization of botanical drugs and to update the botanical names. A total number of 23 species (16 indigenous and 7 exotic) belonging to this genus were studied, which constitute all the species recorded in the main and regional Sudanese Floras besides the species deposited at various herbaria of the Sudan. A taxonomic review of these species has been made and the Latin names have been updated. The species were studied using various macroscopic and microscopic attributes. The macroscopic attributes included the morphology of vegetative and reproductive parts, while the microscopic attributes included palynology and anatomy of certain selected organs. In the palynological study, both Light Microscope (LM) and Scanning Electron Microscope (SEM) have been used to elucidate the various features of the pollen grains of the genus. Medical uses and active constituents of the studied species have also been reviewed.