Rhamnus purshiana, and Frangula purshiana.  Cascara Bark, Sagrada, Sacred Bark   Family: Rhamnaceae  
The dried bark of cascara has been used for centuries as a laxative, first by Native Americans in the Pacific Northwest, and then by European/U.S. colonizers. The chemicals primarily responsible for the laxative action are the hydroxyanthracene glycosides (particularly cascarosides A, B, C and D), and emodin. These act as stimulant laxatives, with the hydroanthracene glycosides stimulating peristalsis, and emodin exciting smooth muscle cells in the large intestine. Cascara was found in more drug preparations than any other natural product in North America, and is believed to be the most widely used cathartic in the world.[4]
PART USED: Bark- dried and stored at least 1 year before use, to eliminate constituents which cause griping. Collection is made in the early summer and dried.
TASTE: Bitter and persistant.  ODOR: Characteristic. Leathery.
ACTIONS
GROUP: The Gastro-Intestinal Tract- Cathartics
1. Purgative- mild.[1] Laxative tonic.[5]
2. Alterative.[2]
3. Bitter tonic.[2]
INDICATIONS
1. Acute or chronic constipation,[1] especially with hemorrhoids.[2] Anorexia.[2] Dyspepsia.[2,5] Habitual constipation.[5] Digestive complaints.[5]
2. Hemorrhoids.[2,5]
3. Liver and Gall bladder disorders generally.[2]
4. Rheumatism.[2]
5. Pancreatic disorders.[2]
CONTRAINDICATIONS: Should only be used short term, around seven days.[3]
COMBINATIONS
- Constipation, use with Cassia Fruit, Berberis, Licorice and Ginger.[1]
PREPARATIONS -
Bark usually supplied in quilled or curved pieces, about 1-5 mm or more thick, purplish-brown, furrowed longitudinally, with transverse lenticels, and lichens and mosses visible as silver-grey or greenish patches. The inner surface is reddish-brown, darkening with age.
Powdered bark 1-2.5 g.[5]
Cascara dry extract 100-300 mg.[5]
Fluid Extract 1:1 in 45% alcohol,[6] (BPC1973)  2-5 ml on at bedtime.[1,2]
Caution- excessive intake may result in hypokalemia.[1]
    

ORIGIN: British Columbia, Western North America from southern British Columbia south to central California, and eastward to northwestern Montana.
References
Constituents