Buckthorn, known botanically as Rhamnus cathartica (natural order Rhamnaceae), a much-branched shrub reaching 10 ft. in height, with a blackish bark, spinous branchlets, and ovate, sharply-serrated leaves, 1 to 2 in. long, arranged several together at the ends of the shoots. The small green flowers are regular and have the parts in fours; male and female flowers are borne on different plants. The fruit is succulent, black and globose, and contains four stones. The plant is a native of England, occurring in woods and thickets chiefly on the chalk; it is rare in Ireland and not wild in Scotland. It is native in Europe, north Africa and north Asia, and naturalized in some parts of eastern North America. The fruit has strong purgative properties, and the bark yields a yellow dye.

An allied species, Rhamnus Frangula, is also common in England, and is known as berry-bearing or black alder. It is distinguished from buckthorn by the absence of spiny branchlets, its non-serrated leaves, and bisexual flowers with parts in fives. The fruits are purgative and yield a green dye when unripe. The soft porous wood, called black dogwood, is used for gunpowder. Dyes are obtained from fruits and bark of other species of Rhamnus, such as R. infectoria, R. tinctoria and R. davurica - the two latter yielding the China green of commerce. Several varieties of R. Alaternus, a Mediterranean species, are grown in shrubberies.

Sea-buckthorn is Hippophae rhamnoides, a willow-like shrub, 1 to 8 ft. in height, with narrow leaves silvery on the underside, and globose orange-yellow fruits one-third of an inch in diameter. It occurs on sandy seashores from York to Kent and Sussex, but is not common.

American buckthorns are: Rhamnus purshiana or Cascara sagrada, of the Pacific coast, producing cascara bark, and R. Caroliniana, the alder-buckthorn. Bumelia lycioides (or lanuginosa) is popularly called "southern buckthorn."