This diverse genus is native throughout the tropics, with a small number of species in temperate regions.

[12] The tribe Cassieae contains 21 genera and is now known to be polyphyletic,[11] but the classification is still accepted because a revision of Fabaceae has yet to be published.

[14] Philip Miller segregated Senna from Cassia in 1754 in the fourth edition of The Gardeners Dictionary.

[15] Until 1982, many authors, following Linnaeus, did not recognize Senna and Chamaecrista, but included them in a broadly circumscribed Cassia sensu lato.

Phylogenetic analyses of DNA have shown that Chamaecrista, Cassia, and Senna are all monophyletic, but the relationships between these three genera have not been resolved.

from the middle Eocene epoch has been described from the Rancho clay pit in Henry County, Tennessee, United States.

[16] The genus name derives from the Arabic sanā, describing plants whose leaves and pods have cathartic and laxative properties.

Cassia gum, an extract of the seeds of Chinese senna (S. obtusifolia), is used as a thickening agent.

[23] Plants in the Senna genus have been studied for their beneficial effects arising from the abundance of phytochemicals, bioactive components and antioxidant and antimicrobial properties.