Cassic

Rhein, also known as cassic acid, is a substance in the anthraquinone group obtained from Rhubarb. Like all such substances, rhein is a cathartic. Rhein is commonly found as a glycoside such as rhein-8-glucoside or glucorhein. Rhein was first isolated in 1895. It is found in rhubarb species like Rheum undulatum and Rheum palmatum as well as in Cassia reticulata.