Trees and Shrubs of the Eloise Butler Wildflower Garden

Common Buckthorn is an introduction from Europe two centuries ago by the nursery trade, for use as hedge material, that is now the scourge of every woodland in the entire United States and Canada north of the southern tier of U. S. states. There is variability in the leaves and flowers as explained below.

Stems and bark: Growing as a small shrub or to a 20 foot tall tree, the plant is identifiable on younger specimens by the dark bark marked with lenticels (raised portions of bark that are air pores). Old bark is dark gray, scaly and blocky. Sapwood is pink and heartwood is yellow to orange. There are spiny tips on many branches. Bark on young twigs and stems is gray to reddish brown. Buds are reddish-brown to dark brown and appressed to the twig. Twigs angle in many directions.

Leaves are dull green, elliptical to oval, stalked, with a round base, blunt tip and a toothed edge. They have 2 to 4 pair of up-curved veins. Most are opposite but some can be sub-opposite. Leaves are usually restricted to the branch tips. The leaves will remain until frost, thus in late fall Buckthorn is easily identified by their presence.

The inflorescence is a dense cluster (a fascicle) at the leaf nodes of the current years growth just after the leaves unfold. Buckthorn is dioecious, that is, the male and female flowers are on different plants, however, a few plants may have perfect flowers.

Flowers are small, 1/4 inch wide, with a yellow-green calyx that has 4 spreading lobes and 4 inconspicuous petals. Male (staminate) flowers usually number 2 to 8 per cluster (but may have up to 40) and have 4 stamens. Stamens have reddish brown filaments and yellow anthers. The female (pistillate) flowers usually number 2 to 15 per cluster (but may have up to 30) and have 4 styles united until just below the tip. At the base sepals, surrounding the ovary, is a reddish nectar ring.

Fruit: Fertile flowers mature to blue-black 1/4 inch drupes in late summer. Each contains 3 to 4 egg shaped black seeds, 5 to 6 mm long, that are flattened on one side and tapering to a short beak. The seeds are long lived and were it not for the birds that love the berries, control would be easier, but our avian friends spread the seeds from within the berries far and wide. The drupes have strong laxative properties - even for birds.

Habitat: Like many invasive plants, Common Buckthorn adapts to a wide variety of habitats - from dry open areas, to woodlands, to moist wet meadows. As it grows best in full sun, it is usually restricted to woodland edges. Roots are not deep, but are angled making pulling difficult. Once established the dense growth of seedlings crowd out all other plants. Eradication by hand pulling is necessary for smaller seedlings as the roots will re-sprout new stems if not removed or killed. Large specimens must have the cut trunk treated to prevent re-growth. Controlled areas must be revisited as seeds in the soil will continue to sprout as long as they are viable, which may be up to 10 years.

Names: The genus, Rhamnus, is an old Greek name for Buckthorn. The species name, cathartica, refers refers to a purgative, which the berries are if eaten. The author name for the plant classification, 'L.', refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.

Comparisons: Common Buckthorn is most easily confused with the native Alder-leaf Buckthorn, Rhamnus alnifolia, where the leaves also have serrated edges but differ with 5 to 7 pairs of leaf veins, the flowers are 5-parted and the stems are thorn-less. Another invasive species is Glossy Buckthorn, Frangula alnus, whose leaves are not serrate, but shiny, and the berries develop along the branch going through a red stage before turning black, the flowers are 5-parted and the branches do not have thorns. All three retain their green leaves late into autumn when most deciduous species have shed theirs.