By CELESTINE DUNCAN, Editor
Common buckthorn (Rhamnus cathartica) and glossy buckthorn (Frangula alnu [Rhamnus frangula]) are non-native, deciduous, woody shrubs or small trees that were introduced to North America as ornamentals, hedge-row plantings, shelterbelts, and wildlife habitat. Alderleaf buckthorn (Rhamnus alnifolia) is a deciduous, native shrub or small tree. It is a desirable native plant that is not invasive, and plays an important role in the ecosystem. The three species of buckthorn overlap in their distribution and habitat in North America.
Distinguishing between non-native and native buckthorn is important so that management efforts can be targeted appropriately. The following description separates the two invasive buckthorns from the native alderleaf buckthorn.
Common buckthorn (Rhamnus cathartica)
- Shrub to small tree: up to 25 feet tall
- Leaves are dark-green, oval, 1.5-3 in. long. Edges slightly toothed, with 3 to 4 pairs of curving veins. Tip is sometimes folded. Mostly sub-opposite leaf arrangement.
Photo: Chris Evans, Univ. Ill, Bugwood.
- Bark is dark gray and the inner bark is orange (easily seen when the tree is cut).
- Twigs are usually tipped with a sharp thorn.
- Flowers are yellow-green, have four petals, and develop in clusters of 2 to 6 near the base of the petioles.
Photo: Leslie J. Mehrhoff, U.Conn., Bugwood.
- Fruit (drupes) are small purple to black, and contain 4 seeds.
Glossy buckthorn (Frangula alnus)
- Shrub to small tree: up to 23 feet tall
- Leaves are dark green and glossy above, oval, and generally alternate with distinct parallel lateral veins, lack toothed margins.
Photo: Leslie J. Mehrhoff, U.Conn., Bugwood
- Bark is gray to brown, with small, whiteish openings (lenticels).
- Twigs and stems lack thorns.
- Flowers are white, occur in small clusters and have five petals.
Photo Rob Routledge, Sault College, Bugwood.org
- Fruit (drupes) are light green ripening to red then black in late summer, contain 2 to 3 seeds.
Note: Glossy buckthorn has been sold by the nursery trade as three cultivars: Columnaris, Aspenifolia and Ron Williams.
Alderleaf buckthorn (Rhamnus alnifolia)
- Shrub: up to 8 feet
- Leaves are alternate, 1-4 in. long, with slightly toothed edges, and have 5 to 8 pairs of parallel leaf veins.
- Young branches have downy-gray hair, maturing to dark grayish-brown; lack thorns.
- Flowers are greenish-yellow, with five sepals and no petals.
- Fruit (drupes) ripen to a bluish-black and contain 3 seeds.
Photos: Rob Routledge, Sault College, Bugwood.org
Note: Other buckthorns native to North American include: Carolina buckthorn (R. caroliniana) in the east, cascara buckthorn (R. purshiana), California buckthorn or coffeeberry (R. californica) (evergreen) and hollyleaf buckthorn (R. crocea)(evergreen) in the West.