|Figure 35.Cascara buckthorn (Rhamnus purshiana)|
Habitat and range.This native tree occurs on the sides and bottoms of canyons from the Rocky Mountains to the Pacific Ocean, extending north into British America.
Description.The cascara tree is usually from 15 to 20 feet in height. The rather thin leaves are from 2 to 6 inches long and about 1 to 3 inches wide, somewhat hairy on the lower surface and rather prominently veined. The small, insignificant greenish flowers are produced in clusters and are followed by black, 3-seeded berries of a somewhat insipid taste. The bark has a somewhat aromatic odor and an extremely bitter taste. In the cascara district several other species of Rhamnus occur which are not commercially important, but their resemblance to R. purshiana may lead inexperienced persons to include the bark of such species in their collections.
Part used.The bark collected during the summer. The collecting season opens about the end of May and closes before the rainy season sets in, as bark collected after exposure to wet weather is difficult to cure properly. The strips of bark after removal from the trees are dried in such a way that the inner surface is not exposed to the sunlight, in order to retain its yellow color. Cascara bark must be aged at least one year before it is used. If collectors in removing the bark allow enough to remain to prevent the tree from dying it will develop new bark, thus prolonging the natural supply of this valuable drug which is gradually being exhausted.