Frangula

Frangula is a genus of flowering plants in the buckthorn family, Rhamnaceae. The genus is typically separated from the related Rhamnus in modern classifications and comprises shrubs and small trees. Characteristics commonly used to identify Frangula include simple, alternately arranged leaves without spines, small inconspicuous flowers arranged in terminal panicles, and fruit that develops into black drupes.

Notable species include Frangula alnus (common buckthorn), Frangula purshiana (cascara buckthorn), and Frangula californica (California buckthorn). The genus is native to temperate regions of Europe, western Asia, and parts of Africa, with some species extending into North America. Several species have been introduced elsewhere as ornamentals.

Ecology and distribution: Frangula species are adaptable to a range of soils and light conditions. Some species, particularly Frangula alnus, are considered invasive in North American woodlands and wetlands, where dense thickets can suppress native vegetation and alter habitat structure. Birds readily disperse the berries, aiding spread.

Uses and toxicity: The bark of several Frangula species has a long history of use in herbal medicine as a laxative; cascara sagrada, derived from Frangula purshiana, is a well-known example. Laxative activity arises from anthraquinone glycosides present in the bark. Fruits are generally poisonous to humans in large quantities, though many bird species consume them.