Buckthorn is a type of shrub or small tree belonging to the genus Rhamnus. It is known for its small, dark berries and thorny branches. Buckthorn is often found in various habitats, including forests, fields, and along roadsides. Some species, like common buckthorn (Rhamnus cathartica), are considered invasive in certain regions, as they can outcompete native plants. The berries of buckthorn are sometimes used in traditional medicine and can be processed into products like jams and jellies. However, caution is advised, as some parts of the plant can be toxic if consumed in large quantities.