Common Buckthorn, Purging Buckthorn, European Buckthorn, Waythorn
Rhamnus cathartica
by Martin (Mort) Schmidt
for Simply Living
Common Buckthorn is an invasive tree, and not a particularly attractive one, so it’s helpful to be able to recognize it if you’re encouraging native growth. A common explanation for the name “buckthorn” is that it has paired buds that resemble the hoofprints of deer, and sharp points at the tips of small twigs.
Common Buckthorn was introduced to the United States in the early 1800s as an ornamental tree, or shrub. But as the common name “Purging Buckthorn”, and the Latin name, R. cathartica suggest, it was also once valued for its cathartic (laxative) properties, and might have been imported for medicinal purposes. Buckthorn medicine is now discouraged because it can bring on violent purging, and as an aggressive non-native, I recommend you purge Purging Buckthorn.
The first question when identifying non-conifers on a key, is whether the leaves and branches are opposite or alternate. Oppositely-arranged leaves and branches are attached directly across from each other, while alternately-arranged leaves and branches are not. The difference is usually clear-cut, but with Common Buckthorn it isn’t. They tend to have an opposite arrangement, but there are many exceptions, with a resulting pattern that’s sometimes called, “sub-opposite”. The leaves are simple, meaning that they’re attached directly to the tree. Compound leaves have multiple leaflets sharing a stem with other leaflets in consistent groupings of 3, 5, 7, etc., depending on the species.
Common Buckthorn leaves are pinnately-veined (feather-like), i.e., they have a single primary vein, with secondary veins attached to it at various points. Palmately-veined (hand-like) leaves have multiple primary veins attached at the base. More precisely, Common Buckthorn leaves have arcuate veining, in which the veins diverge from the central vein, curve, and run parallel to the outer edge. The dogwoods, including Flowering Dogwood (Cornus florida) are also recognizable by their arcuate veins. R. cathartica leaves are 0.75 to 2.5 inches long, and 0.75 to 2 inches wide. The leaves are elliptical, and have small teeth – but not as small as those on Flowering Dogwood, which are barely visible to the naked eye. Buckthorn leaves are smooth and green, and turn brown in winter, unlike dogwood leaves, which turn red. Buckthorn leaves occur before most other trees in the spring, and remain on the tree after most other leaves have fallen.
Complicating matters is the fact that there are multiple native dogwoods in Ohio. Lucy Braun’s The Woody Plants of Ohio lists 10 species, and all have similar leaves. But except for Flowering Dogwood, the others are limited to shrubs.
Purging Buckthorns have small flowers with 4 petals in the spring. The flowers could never be confused with the far larger, showier flowers on Flowering Dogwood. In summer, the flowers produce dense clusters of ¼ to ⅜-inch spherical green berries, turning purple to black when ripe. Common Buckthorn is dioecious, so fruits occur only on female trees. Flowering Dogwood berries are elongated and turn red when ripe.
Bark is perhaps the best way to distinguish Common Buckthorn from dogwoods. Buckthorn bark is brown, has a somewhat metallic sheen and faint horizontal bands of pores known as lenticels. The bark often peels off to reveal reddish layers. Exposing the inner bark with a knife reveals a distinct yellow to orange color. Sharp spines are also present, though not nearly as prominent as those on Callery Pear (Pyrus calleryana) or Honeylocust (Gleditsia triacanthos). According to the Penn State Extension, Common Buckthorn lacks true thorns or spines, but small twigs at the ends of branches typically break off to form a sharp point.
The tree-sized Flowering Dogwood has distinct bark that breaks up into small polygons.
The name “buckthorn” is applied to a number of trees from multiple species and genera. Flowers in genus Rhamnus, which includes R. cathartica, have 4 petals, while flowers in genus Frangula have 5 petals. But the leaves, fruits, and other traits are similar enough that some species occur in the literature under either name. Rhamnus and Frangula are in the same family, Rhamnaceae. Once again, we’re reminded that the classification of trees, or for that matter, just about anything, is malleable, and there isn’t a single correct way to do it.
Mature Common Buckthorns typically have a height of 20 to 25 feet and a trunk diameter of approximately 0.5 feet. Ohio’s Champion European Buckthorn, located in Wayne County, has a height of 32 feet, a trunk diameter of 1.5 feet, and a crown width of 40 feet.
ID Summary: Small tree or shrub with arcuately-veined, sub-oppositely arranged toothed leaves, yellow or orange inner bark, sharp spines, numerous dark berries, bark with horizontal lenticels, small green flowers with 4 petals.
Similar Trees: Most dogwood species have distinctly opposite leaves. Ohio native Carolina Buckthorn (Frangula caroliniana) leaves lack teeth, flowers have 5 petals.
Common Buckthorn has been naturalized over much of the northern U.S., especially in the Northeast. R. cathartica grows in a variety of conditions, but tends to prefer moist soil and sunlight. It can be found in floodplains, fence rows, vacant lots, and abandoned fields.
Purging Buckthorn is native to Europe. Brought to the U.S. in the early 1800s, it is now established throughout the country, but especially in the Great Lake states and the Northeast. Common Buckthorn is not listed in the Columbus, Ohio Street Tree Inventory, but according to the 2020 Chicago Region Tree Census Report, it makes up an astonishing 36% of the tree inventory in the seven-county Chicago area! The second most common tree, Boxelder (Acer negundo) makes up only 4%.
Common Buckthorn lumber has a Janka hardness of 1,040 lbf and a density of 0.61 g/cc, according to the Wood Database, compared to the median of my list of 73 Ohio trees of 1,075 lbf and 0.64 g/cc (on par with Black Walnut – density and hardness based on Cascara Buckthorn (Rhamnus purshiana)). The database goes on to say that buckthorn turns, glues, and finishes well, but is too small to have commercial potential.
Presumably because it was introduced to the U.S. from Europe in the 1800s the Native American Ethnobotany Database (NAED) has very few entries for Rhamnus cathartica. But it does cite Hamel and Chiltoskey’s Cherokee Plants and Their Uses – A 400 Year History, which indicates that the Cherokee used Common Buckthorn as an eyewash, a cathartic, and to treat itches. The NAED also lists uses by numerous Native tribes for other members of the Rhamnaceae family. Most often listed is the use of buckthorns as a cathartic, emetic, or laxative, especially from the roots and bark, but also from the berries. Curiously, several tribes were said to consume the berries for food. Perhaps the berries’ ripeness or the volume consumed determined which purpose they served. Quite a number of tribes used various buckthorn berries, and to some degree, the leaves and bark as a wash for wounds and sore eyes.
Historically, Purging Buckthorn was used as a laxative, but was abandoned due to its tendency to be too effective, resulting in violent diarrhea, cramping, and vomiting. Other members of the buckthorn family were effective but less extreme. The purgative compounds were derived directly from the berries or extracted from bark. Wikipedia states that, “It also appeared to be routinely used as a purgative in some monastic settings, as was clear from the latrine pits of the Benedictine Abbey at St. Albans excavated in the 1920s, where great numbers of buckthorn seeds were found mixed up with the fragments of cloth used by the monks as lavatory paper.”
According to Botanical.com Rhamnus cathartica first appeared in the London Pharmacopoeia of 1650, and was still official in the British Pharmacopoeia of 1867. The same source also tells us that the dried unripe berries were once sold under the name of “French berries” to make a yellow dye for staining maps or paper. When ripe, the berries provided the color known as “sap” or “bladder green” for watercolor paints.
Common Buckthorn serves as a winter host to the soybean aphid, which was introduced to the U.S. in the 1990s, and causes damage to soybean crops. Illinois Wildflowers lists a number of other animals that consume Common Buckthorn, including:
- Buckthorn aphid,
- Robins,
- Gray catbirds,
- Northern cardinals,
- Cedar waxwings,
- Hermit thrushes,
- White-breasted nuthatches,
- European starlings,
- Eastern bluebirds,
- Rose-breasted grosbeaks,
- House finches,
- House sparrows,
- Elk, and
- White-tailed deer.
Unfortunately, these animals help propagate the seeds, and some of them are invasive and would, ideally, not find abundant food.
According to Angelfire.com, Common Buckthorn is said to provide protection from several things, including magic, demons, poisons, and headaches, by placing branches near windows and doors. It is lucky to carry or wear a piece of buckthorn wood, especially for legal matters. Angelfire also states that buckthorn charcoal was ideal for making gunpowder. Sprinkling buckthorn in a circle and dancing in it under a full moon would cause an elf to appear, who would grant you a wish.
And finally, the buckthorn was considered to be a possible source for Christ’s crown of thorns. But this tree hardly needs any more reason to be disliked, at least outside of its native range.
You can also listen to my talks on Ohio Broadleaf Tree Identification on YouTube, Part 1 and Part 2.
