Rhamnus purshiana

Rhamnus purshiana (also known as cascara sagrada) is a species of buckthorn native to western North America, from southern British Columbia south to central California, and eastward to northwestern Montana.

The plant is a large shrub or small tree that grows to 15 m tall with a trunk diameter of up to 50 cm. The bark is brownish to silver-grey with light splotching. The leaves are deciduous, alternate, clustered near the ends of twigs. The flowers are tiny, 4–5 mm diameter, with five greenish yellow petals; they are produced in clusters in the leaf axils in the spring.

The fruit is a drupe 6–10 mm diameter, bright red at first, quickly maturing deep purple or black, and containing a single seed. The seeds are dispersed by birds and mammals.

The bark is harvested commercially for use in medicine. The active ingredients, known as anthraquinones, have a strong purgative effect on the human body. Because of concerns about overharvesting in the wild, the plant is now grown commercially for the medicinal trade.

Medicinal use

The dried, aged bark of Rhamnus purshiana has been used for centuries by Native Americans as a laxative. In modern times, it is used in the treatment of constipation and is considered a safe and gentle remedy. The bark contains compounds called anthraquinones which stimulate the bowel and have a strong laxative effect. The bark is often aged for a year or more to allow the anthraquinones to oxidize, which reduces the bark's laxative effect.

Cultivation

Rhamnus purshiana is grown both for its medicinal properties and as an ornamental plant. It is a hardy plant that can tolerate a range of soil types and climates. It prefers full sun to partial shade and well-drained soil. It is resistant to most pests and diseases and requires little maintenance once established.

Conservation

Overharvesting of Rhamnus purshiana in the wild for its medicinal bark has led to a decline in its population in some areas. Conservation efforts are focused on sustainable harvesting methods and cultivation of the plant for commercial use.