Cascara is a small tree or shrub ranging from BC through Northern California, and East into Montana. In the Eastern and Southern parts of its range, it adopts shrubby forms, some of which may be distinct subspecies.
The scientific name appears to be in transition. While the Integrated Taxonomical Information System still lists it as Rhamnus, many up-to-date sources (Jepson 2nd. Ed.; WTU Herbarium; USDA database) have elevated the subgenus Frangula (thornless buckthorns with five petals and no leaf scales) to the genus level.
The common name Cascara comes from the Spanish “Cascara Sagrada” or “sacred shell”, named for its medicinal bark. The bark of the Cascara is an effective and relatively mild laxative. It was accepted into the western pharmacoepia until 2002, when the FDA banned it for over the counter use, for lack of studies proving its safety. As it is slow-acting, there is danger of overdose, and long term use can cause habituation. Although there are reports of people eating the fruits, they probably contain some toxins. Parts of the cascara plant are also uesd to produce yellow and green dyes.
Cascara has a high value to wildlife. The Lepidoptera Caterpillar Host Plant Database lists 22 species that use Frangula purshiana. A cascara in flower tends to be full of insect pollinators. Many birds, including grosbeaks, grouse and band-tailed pigeons consume the fruits, as do many mammals. However, it ranks as poor forage for ungulates, making it a relatively deer-proof plant.
Cascara most often grows as an understory tree, easily overlooked if you are not paying close attention, though the reddish bark and long, pleated leaves are quite pleasing. Individuals planted in the sun become much fuller than those in the shade. Since there is a market for the bark, large cascaras are rare in the wild. Many harvesters peel off the bark from a standing trunk. This kills the tree. Cutting the tree down and leaving a tall stump allows for substantial bark harvest, and allows the tree to grow back, albeit in a coppiced form.