Buckthorn Bark (Rhamnus frangula) is native throughout the temperate and subtropical Northern Hemisphere, and also more locally in the subtropical Southern Hemisphere in parts of Africa and South America.

Both deciduous and evergreen species occur. The leaves are simple, 3-15 cm long, and arranged either alternately or in opposite pairs. One semi-unique characteristic of many buckthorns is the way the veination curves upward towards the tip of the leaf. The plant bears fruits which are dark blue berries. The name comes from the fact that there is a woody spine on the end of each twig in many species. Buckthorns are used as food plants by the larvae of some Lepidoptera species.

The dried, aged bark of this tree has been used continuously for at least 1,000 years by both native and immigrant Americans as a laxative natural medicine, commercially called "Cascara Sagrada", but old timers call it "chitticum bark".