Japanese buckthorn (Rhamnus japonica) is an exotic weed and invasive plant in Illinois. This shrub spreads by seed, or through fragments of the plant that reproduce elsewhere, known as vegetative growth. It is found in wooded areas like forests or disturbed sites. The species is native to Asia, but today can be found throughout Illinois and Missouri. It grows to a height of about 20 feet. The leaves, flowers, and fruit are relatively similar to that of common buckthorn. Data collected at The Morton Arboretum show that this tree is invasive on the Arboretum grounds. Common chokecherry (Prunus virginiana) is a good alternative.
There are a number of native and non-native species that could be used in place of Japanese buckthorn. To find suitable replacements, go to The Morton Arboretum’s tree and plant finder. Before purchasing or planting, be sure to check for any local or state guidelines, and ensure that it is suitable for its habitat by reviewing planting considerations or by finding it in the USDA Plants Database.
More Information
Size and Method of Spreading
Japanese buckthorn typically grows to be 15 to 25 feet tall. The broad branches form dense thickets.
Bark Color and Texture
The bark is brown to gray in youth. Rough and slightly peeling, the stems have prominent white lenticels and the interior wood is yellow. Stems often have scattered thorns.
Leaf Description
The green leaves are opposite to sub-opposite, 1 ½ to 3 inches long, and ¾ to 1 ½ inches wide. They are long and oval-shaped (elliptical) with minute teeth on the edges (leaf margins), and a pointed tip. The leaves of buckthorn often remain green well into autumn after other trees have dropped their leaves.
Flower Description
Japanese buckthorn’s flower heads develop in clusters of small florets near the branches (raceme inflorescence). Each flower is light green, and has four sepals, forming a crosslike (cruciform) shape. Each plant bears either male or female flowers (dioecious), but some may produce perfect flowers, with both genders as well. Flowering time is early summer.
Fruit Description
Female plants bear ¼-inch berrylike fruits (drupes) in clusters. They are green in summer and turn dark blue to black in August.
General Management
Japanese buckthorn can be managed through mechanical and chemical methods. For more information on management of this plant, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).
