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 native alderleaf buckthorn.
COMMON BUCKTHORN (RHAMNUS CATHARTICA)—INTRODUCED
- 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)—INTRODUCED
- 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) —NATIVE
- 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
Celestine Duncan contributed to this article.