The Lewis & Clark Native Plant Garden of the Idaho Botanical Garden in Boise features a collection of Cascara buckthorn (Rhamnus purshiana) plants of the buckthorn family (Rhamnaceae). A specimen was collected by the Lewis & Clark expedition on May 29, 1806, near Camp Chopunnish along the Clearwater River in Idaho. An information board gives the fiollowing details:
Lewis noted: "A shrub apparently a species of Rhamnnus. About 12 feet high in clumps; fruit a 5-valved purple berry, which the natives eat and esteem highly..."
The bark was boiled and the tea (or syrup) was used by Native Americans tribes as a strong laxative. The bark was harvested in the fall. It was allowed to age before use because the fresh bark was considered to be nauseating.
More on Cascara Buckthorn
Habitat, range, description, usage of Rhamnus purshiana DC.
USDA Plants Profile, Frangula purshiana (DC.) Cooper (Cascara buckthorn)
VirginiaTech on Cascara buckthorn (symbol: FRPU7): Leaf, flower, fruit, twig, bark, form