Cassia is a genus of flowering plants in the legume family, Fabaceae, and the subfamily Caesalpinioideae. Species are known commonly as cassias. Cassia is also the English common name of some species in the genus Cinnamomum of the family Lauraceae. Many species of genus Senna were previously included in Cassia.ecause the name Cassia is not precise, it is sometimes difficult to know what is meant by references to plants known as cassias.