Common Buckthorn (Rhamnus cathartica), also known as European Buckthorn, is an invasive shrub found throughout Ohio, the greater Midwest, and a large portion of the eastern United States. Its ability to colonize fence rows, fields, and neglected areas -- coupled with its tough constitution and rapid growth rate -- allows it to quickly produce copious amounts of black fruits on relatively young female shrubs. It is spread via bird consumption and subsequent dispersal to surrounding areas, much like Amur Honeysuckle. These two foreign shrubs often occupy the same niche, displacing native shrubs and trees. The most positive aspect of this large shrub or small tree is its glossy, dark green foliage, which is usually not bothered by pests. The leaves usually hang on late into autumn. Its heartwood is bright orange, and its wood strongly resists rotting.
Common Buckthorn is named for the semi-thorny nature of its short twigs, which terminate in modified spines rather than buds. The specific epithet refers to a cathartic drug that is extracted from the bark. Specimens found in the wild may reach 15 feet tall and 15 feet wide; those limbed up and thinned of smaller trunks at the base may grow to 25 feet tall by 20 feet wide. As a member of the Buckthorn Family, it is related to other Buckthorns, including two that are used in modern landscapes.
Potential Problems - Common Buckthorn is extremely invasive via the production, dispersal, and germination of its many seeds, which female shrubs start producing at a young age. In the first two years of its life, its black roots are shallow and fibrous, making them easy to pull up. In addition, Common Buckthorn serves as the alternate host for a type of fungal rust (Puccinia coronata) that devastates oats and other cereal grains.
Identifying Features - Common Buckthorn
Common Buckthorn leaves have veins that are unusual in that they branch in alternate fashion from the midrib, then run roughly parallel to the serrated leaf margins. Leaves may be either orbicular (top) or elliptical (bottom). Fall color is green or chartreuse, then abscising.
Common Buckthorn is classified as having opposite leaves and buds, but they also can be subopposite (not exactly "opposite" but also not far enough apart to be considered "alternate"). Common Buckthorn shares this rare quality with Forsythia (a landscape shrub).
Common Buckthorn is a dioecious species, having small yellow-green male and female flowers on separate trees. On female trees, these become clusters of small, rounded, green fruits, which change to plump black fruits by late summer. Birds relish the fruits and spread the seeds to areas where they easily germinate the following spring.
The terminal buds of many twigs of Common Buckthorn are actually modified spines and give a thorny character to this noxious shrub (three spines are shown). This shrub also has many spur shoots from which many leaves, flowers, and fruits arise.
The young bark is smooth and shining with brown-gray bark that has prominent small lenticels. Mature bark is also shiny, but it becomes more scaly with horizontal lenticels.