Rhamnus purshiana (Cascara Buckthorn, Cascara, Bearberry, and in the Chinook Jargon, Chittam or Chitticum; syn. Frangula purshiana, Rhamnus purshianus) is a species of buckthorn native to western North America from southern British Columbia south to central California, and inland to western Montana.
It is the largest species of buckthorn, occasionally growing up to 15 m tall, though more commonly a large shrub or small tree 5–10 m tall, with a trunk 20–50 cm in diameter. The bark is brownish to silver-grey with light splotching. The leaves are deciduous, alternate, clustered near the ends of twigs; they are oval, 5–15 cm long and 2–5 cm broad with a 0.6–2 cm petiole, dark shiny green on top, fuzzy and paler green below. The flowers are tiny, 4–5 mm diameter, with five greenish yellow petals; the flowering season is brief, disappearing by early summer. The fruit is a berry 6–10 mm diameter, bright red at first, quickly maturing deep purple or black, and containing three seeds.
It grows in moist, acidic soils in the shady side of clearings or in the marginal forest understory, near the edges of mixed deciduous-coniferous forests. It typically grows as a second-generation tree after alders have colonized a barren plot of land.
The dried, aged bark of this tree has been used continually 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". The laxative action is due to the Cascara glycosides(cascarosides A,B,C & D).
Cascara Sagrada means "sacred bark" in Spanish. The much more pertinent name chitticum means "shit come" in Chinook Jargon; chittam comes from the Chinook Jargon phrase chittam stick = "laxative tree" which is similarly from the English word "shit".
Long used as a laxative by Native American groups of the northwest Pacific coast, chitticum bark or Cascara Sagrada was accepted in medical practice in the United States in 1877, and by 1890 had replaced the berries of the European Buckthorn (R. catharticus) as a commonly used laxative. It was the principal ingredient in many commercial, over-the-counter laxatives in North American pharmacies until 9 May 2002, when the U.S. Food and Drug Administration issued a final rule banning the use of aloe and cascara sagrada as laxative ingredients in over-the-counter drug products. Use of Cascara Sagrada has been associated with abdominal pain and diarrhea and is potentially carcinogenic.
The bark is harvested mostly from wild trees; over-harvesting in the middle 1900s eliminated mature trees near many settled areas. Once stripped from the tree, the bark is aged for about 1 year to make its effect milder. Fresh cut, dried bark causes vomiting and violent diarrhea.