Common buckthorn (Rhamnus cathartica), also known as European waythorn, European buckthorn and Hart's thorn, is a shrub or small tree that grows up to 22 feet in height. It is considered an invasive species in most areas of the United States and southeastern Canada due to its tendency to form dense thickets that crowd out native plants.
Leaves and Branches
Common buckthorn leaves are dark green, glossy and have jagged, finely-toothed margins. Each leaf has three to five pairs of curved veins. The leaf surfaces do not have any hairs. Common buckthorn leaves stay green until the late fall, long after most other deciduous trees have shed their leaves. The leaves and buds are arranged opposite along the branches. Twigs tend to end in a sharp, stout thorn, or "spine." A spine may also be found in the fork between two branches.
Bark and Wood
Common buckthorn bark is grey to brown, with elongate, silvery, prominent, rough-textured projections. It is frequently confused with the bark of plum or cherry trees. When cut, the wood exposes yellow sapwood and pink to orange heartwood. In the winter, the tree is naked except for hairy terminal buds and arched twigs that have leaf scars, which provide a bumpy silhouette.
Flowers and Fruit
Dense clusters of two to six small, yellowish-green, four-petaled flowers form on the stems near the bases of the leaves in the late spring. A common buckthorn tree will bear either male or female flowers. Female plants are recognisable by their fruit. They bear clusters of deep, purplish-black berries. The fruits are 1/4 inch in diameter, and ripen in August and September. Each berry contains four seeds.
A similar invasive species, glossy buckthorn (Rhamnus frangula), looks much like common buckthorn, with some differences: no spine at the tip of its twigs, leaves that have smooth margins rather than toothed and leaf undersides that are hairy. Common buckthorns and glossy buckthorns are often confused with native American buckthorns, including Carolina buckthorn (Rhanmnus caroliniana), alder buckthorn (Rhamnus alnifolia) and lance-leafed buckthorn (Rhamnus lanceolata). These native species are not threatening to the environment.