Rhamnus cathartica aka Common Buckthorn

Rhamnus cathartica is known as common or European buckthorn. It belongs to the buckthorn family, Rhamnaceae. Its native range spans Europe, parts of Asia, and northwestern Africa. It is native to Britain and Ireland. People brought it to North America in the early 1800s. It now grows wild across much of eastern North America. It forms a large shrub or small tree and sheds its leaves.

Garden plants often reach 16–25 feet [4.9–7.6 metres] tall. Some sources report heights of 30 feet [9.1 metres]. One garden source gives a spread of 15 feet [4.6 metres]. Others describe plants almost as wide as they are tall. The crown is rounded, with several stems and suckering growth. Small thorns end many shoots. Older bark turns dark brown or gray and peels. Pale lenticels mark its surface, while the inner bark is orange. The simple, oval leaves have toothed edges and curved veins. Leaves may sit opposite, nearly opposite, or alternate along stems. They stay green late into fall, then turn yellow or yellow-green.

Small yellow-green flowers open from April to June. Male and female flowers grow on separate plants. Bees visit the flowers, which offer little show. Female plants bear round, fleshy drupes with two to four seeds. The fruit ripens to glossy black in fall. Birds eat the fruit and carry seeds to new sites. Seeds also fall near the parent plant and form dense growth.

It grows fast in sun or part shade. It also tolerates deeper shade and a wide range of soils. Moist soil with good drainage suits it best. It tolerates drought, though steady moisture supports growth. RHS lists acidic, neutral, and alkaline soils as suitable. Sources give USDA zones 3–8 and UK hardiness H7. Past uses include hedges, screens, windbreaks, and woodland plantings. Its fruit and bark yield dyes. Its hard wood serves for small turned objects.

Its spread can crowd out native plants and change habitats. Established plants are hard to remove and regrow from stumps. Missouri Botanical Garden advises against new landscape planting. Reported problems include leaf spot, mildew, rust, aphids, and scale. Honey fungus occurs rarely, and it hosts oat crown rust. No edible uses are known. Eating fruit can cause nausea, vomiting, and diarrhea. It can harm people and dogs. Past medicinal use relied on strong laxative effects, which can be harsh.