Frangula is a genus of about 50 accepted species of shrubs or small trees, commonly known as buckthorns in the family Rhamnaceae. They are deciduous with alternate, simple leaves with stipiles, buds without bud scales, branches without spines and flowers with five petals and undivided styles. The fruits are 2 to 4-seeded berries.
Several plants long considered in the genus Rhamnus are now included in the genus Frangula. This change, which is supported in part by genetic evidence, is generally accepted by taxonomic authorities.
The difference between Frangula and Rhamnus has long been recognized, but treatments in taxonomic rank have been inconsistent. Frangula was treated within Rhamnus, sometimes as a subspecies, but it was also noted that Frangula and Rhamnus are more closely related to each other than to other taxa. This observation has been corroborated by molecular studies that show them as sister taxa. Frangula contains about 50 species, including 7 North American species. (Flora of North America)