Rhamnus is a genus of about 150 species (fewer, if some species are placed in Frangula), which are shrubs or small trees, commonly known as buckthorns. It is part of the family Rhamnaceae. Its species range from 1 to 10 meters tall (rarely to 15 m) and are native mainly in east Asia and North America, but found throughout the temperate and subtropical Northern Hemisphere, and also more locally in the subtropical Southern Hemisphere in parts of Africa and South America.
Both deciduous and evergreen species occur. The leaves are simple, 3 to 15 centimeters long, and arranged either alternately or in opposite pairs. One distinctive character of many buckthorns is the way the veination curves upward towards the tip of the leaf. The plant bears fruits which are black or red berry-like drupe. The name is due to the woody spine on the end of each twig in many species.