Ramnus cathartica, or common buckthorn, is a shrub or small tree native to Europe. Its name is derived from the spines that grow at the tips of its branches. Introduced to North America in the 19th century as a hedge plant, as of 2014, it's classified as an invasive species.
Buckthorn spreads readily with the help of birds and animals that ingest its seeds and disperse them in droppings. The plant grows from 20 to 25 feet in height and leafs out early in the spring, shading out native competitors. Buckthorn also produces chemical compounds that inhibit the growth of other vegetation. The plant is particularly aggressive in wetland areas and serves as a host for agricultural pests, including soybean aphids and the fungus that causes oat rust.