Frangula Genus

Frangula is a genus of approximately 56 species of flowering shrubs and small trees in the family Rhamnaceae (order Rosales), commonly known as buckthorns. The genus is most closely related to Rhamnus, with which it shares the buckthorn common name, and is entirely distinct from the superficially similar sea-buckthorn (Hippophae rhamnoides) of the family Elaeagnaceae.

Species range from deciduous to evergreen and grow from compact shrubs to small trees reaching up to 12 metres in height, as in Frangula purshiana (cascara buckthorn). The bark is characteristically dark grey-brown to blackish. Leaves are alternate and simple, with stipules; branches lack spines and buds lack bud scales — features that help distinguish Frangula from Rhamnus, whose species often bear thorny branchlets. Flowers are small, typically bearing five petals (compared with the usually four-petalled flowers of Rhamnus), with undivided styles. The fruit is a fleshy berry containing two to four seeds, dispersed primarily by birds.

The genus was long treated as a subgenus of Rhamnus but is now increasingly recognised as a distinct genus in its own right, with Frangula alnus Mill. (alder buckthorn) designated as the lectotype species. The genus has a near-cosmopolitan distribution, occurring throughout most of Europe and the Americas, large parts of Asia, and the far northwest of Africa. It is absent from sub-Saharan Africa, the Indian Subcontinent, and Australasia.

Alder buckthorn (F. alnus) was of major historical importance in Europe: its charcoal was regarded as the finest available for gunpowder manufacture from the 15th to the 19th centuries. California buckthorn (F. californica), also known as coffeeberry, is a notable western North American species widely used in native plantings. As with Rhamnus species, the berries of Frangula are a powerful purgative and have been used medicinally.