Buckthorn: Accurate Identification

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- Buck-thorns are thicket-forming, invasive small trees that crowd out native species in forests and natural areas.

There are two buckthorn species we'll consider as a group because they behave similarly in the landscape and require similar control procedures European, or common buckthorn, introduced from Europe, and glossy buckthorn, introduced from East Asia.

Both species' showy fruit display and hardy foliage made them popular ornamentals, but they are now highly competitive invaders of eastern woods and wetlands.

Both species have established throughout the U.S., particularly in the lake states and the Northeast.

The name buckthorn references the habit young branches have of breaking off to form what appear to be sharp thorns, though neither species bears true spines or thorns.

Let's first look at the identification characteristics for the European or common buckthorn.

Trees of this species can grow to reach 25 feet in height.

The leaves are football shaped, sub-oppositely arranged, finely toothed on the edges or margins, and show distinct, arcing veins.

The stems of common buckthorn have a metallic, silver-brown bark, creating a gunmetal look.

Twigs are often tipped with an apparent spine.

The mainstem exhibits many horizontal ridges, called lenticels, and the inner bark is a vibrant yellow.

Flowers on common buckthorn are greenish yellow have four petals and are less than 1/2 an inch across, growing all along the stem.

This species is dioecious, meaning there are separate male and female plants.

Common buckthorn fruit ripens in the fall and is round and deep purplish black, about a 1/2 inch in diameter.

While only female plants produce fruit, one plant can be highly productive.

Now let's take a closer look at glossy buckthorn, which grows up to 20 feet tall.

Glossy buckthorn's leaves are also football shaped, but they're alternately arranged with curved, parallel veins.

They're tough, leathery, and glossy in appearance.

Unlike common buckthorn leaves, glossy buckthorn leaves have a smooth, toothless leaf edge or margin.

Smaller stems on glossy buckthorn are smooth and silver gray.

Larger stems show a mottled texture created by white lenticels.

Young growth and buds on the species are covered in fuzzy brown hairs.

The flowers on glossy buckthorn are greenish yellow, have five petals, and are less than 1/2 inch across, growing all along stem.

In contrast with common buckthorn, glossy buckthorn is monoecious, with both male and female reproductive structures on one plant.

Glossy buckthorn's round fruit is about 1/2 inch in diameter.

It ripens throughout the growing season, from green to red to dark purple or black.

You may find multiple stages of fruit ripening present on one plant at one time.

Buckthorns of both species are primarily spread by birds dispersing their abundant and highly-visible fruit.

The fruit often persists into winter, even after the leaves drop, when it becomes even more visible to birds and mammals for foraging.

Buckthorn's tolerance of deep shade is at the core of its success in invading natural habitats, particularly forests.

Though buckthorn can also grow in full or partial sun, it thrives in forest interiors where there's less competition from other less shade-tolerant understory shrubs.

Common buckthorn is most often found invading open woodlands and forest edges.

Glossy buckthorn, on the other hand, trends more toward occupying wetlands, but it can also establish on dryer sites.

Once they colonize these spaces with their dense, low canopy, other vegetation is shaded out, resulting in a buckthorn thicket.

There are some lookalikes you might confuse with buckthorn.

Native dogwoods have very similar leaves to those of common buckthorn, with their distinct arcing venation.

But to distinguish them, notice that native dogwoods have an opposite branch structure and smooth leaf margins, while common buckthorn has sub-opposite branching and finely-toothed leaf margins.

Similarly, smooth alder can also be easily confused with glossy buckthorn, but alder leaves have a roughly toothed margin compared to glossy buckthorn's smooth leaf edge.

Additionally, throughout much of the year, smooth alder holds soft cone-like structures, called catkins, which are very different from the flower and fruit structures of glossy buckthorn.

Buckthorn requires active management to prevent it from taking over natural areas and displacing native plant communities.

The first step to controlling any invasive species is learning how to identify it.

And now that you can positively identify buckthorn, consider applying control measures where you find it.