Senna consists of the dried leaflets or fruits of Cassia senna (C. acutifolia) known in commerce as Alexandrian senna and of Cassia angustifolia commonly known as Tinnevelly senna. The senna plants are small shrubs of Leguminosae cultivated either in Somalia, the Arabian peninsula and near the Nile river. Tinnevelly senna is obtained from cultivated plants mainly in South India and Pakistan. Owing to the careful way in which the plant is harvested, the leaflets of the drug are usually little broken. Damaged leaves and lower quality products are often used for making galenicals. The senna pods (fruits) are collected during the same period as the leaves, then dried and separated into various qualities. The active principle of Senna was first isolated and characterized by Stoll in 1941. The first two glycosides were identified and attributed to the anthraquinone family. These were found to be dimeric products of aloe emodin and/or rhein which were named sennoside A and sennoside B. They both hydrolyze to give the aglycones sennidin A and B and two molecules of glucose. Later work confirmed these findings and further demonstrated the presence of sennosides C and D. Small quantities of monomeric glycosides and free anthraquinones seem to be present as well. The active constituents of the pods are similar to those of the leaves but present in larger quantities. Two naphthalene glycosides isolated from senna leaves and pods are 6-hydroxymusicin glucoside and tinnevellin glucoside. Both compounds can be utilized to distinguish between the Alexandrian senna and the India senna, since tinnevellin glucoside is only found in the latter and the first only in the C senna. Finally, a series of other compounds has been isolated from senna such as the yellow flavanol kaempferol, its glucoside kaempferin, isorhamnetin, further sterol glucosides, mucilage polysaccharides, resin and calcium oxalate. Detailed studies on the water-soluble polysaccharides reported the presence of several distinct hydrocolloids.