Common buckthorn (Rhamnus cathartica)
Common Buckthorn (also known as European Buckthorn) is a deciduous shrub or small tree native to Europe and Asia. This species was introduced to Canada in the late 1880’s as a farmstead windbreak species and an ornamental shrub1. Since its introduction, Common Buckthorn has spread aggressively across Canada and is now found from Nova Scotia to Saskatchewan2. Buckthorn is found throughout the Credit River Watershed, and is listed under the Noxious Weeds in Ontario list.
Common Buckthorn is a hardy woody plant species that is capable of growing in a wide range of soil and light conditions, thriving in disturbed habitats such as forests, thickets, and meadows. Common Buckthorn can range in size from a shrub to a small tree, and can grow up to 6 m tall with a diameter of 25 cm1,2. When young, the bark is smooth and dark grey with raised patches, which are known as lenticels. As it matures, the bark becomes rough and begins to peel. The leaves are shiny, green, and opposite to sub-opposite along the stem. The leaves are egg shaped with small rounded teeth along the edges and prominent veins that converge at the tip of the leaf3.
As a dioecious plant species, Common Buckthorn develops male and female flowers on separate plants. In early June, small yellowish-green flowers are produced on female plants. Once these flowers are pollinated, green berries are produced in clusters that eventually ripen to a dark purple/black in late summer. The scientific name for this species, R. cathartica stems from the laxative effect of the fruit: an evolutionary trait that ensures birds will disperse the seeds3.
Thorn on Common Buckthorn twigs
Common Buckthorn threatens biodiversity in natural areas, as it is able to out-compete native and woody herbaceous plants, due to its long growing season, ability to tolerate a wide range of growing conditions, and high reproductive success.
In North America, Common Buckthorn has a longer growing season than native species, allowing it to get a head start to the growing season, by developing leaves weeks before those of native species. Common Buckthorn also holds onto its leaves and berries later into the fall than most native species2. Once space is available, Common Buckthorn seedlings will quickly take over a site, and as they grow, can completely dominate the understory and shrub layer. Euorpean Buckthorn not only out-competes native species, but also changes the soil chemistry making it difficult for other native species to survive3.
Common Buckthorn also poses a threat to agricultural crop yields, as it is a host for two invasive pests: soybean aphids and the fungus that causes oat crown. For this reason, Common Buckthorn is listed as a Noxious Weed in Ontario’s Weed Control Act2.
Early detection and removal is the best strategy for preventing the establishment of Common Buckthorn. Young plants can be removed manually by pulling them out with your hands or with a weed wrench, or digging them out with a shovel. The sharp spines are not usually a problem if precautions are taken, such as wearing gloves. It is crucial to monitor removal sites to ensure any new seedlings are controlled, as Common Buckthorn seeds can remain viable in the soil for up to 5 years3. Chemical control can also be an effective method, especially for large buckthorn stems.
For more information on Common Buckthorn, please contact CVC via email or to report sightings of Common Buckthorn call the Ontario Federation for Anglers and Hunters Invasive Species Hotline at 1-800-563-7711 and add the sighting to the EDDMaps Ontario website.
https://www.youtube.com/watch?v=v0z87y3SsuM (Video created by Montana Weed Control Association)
Links for Further Information:
Ontario Invasive Plant Council’s “Invasive Common (European) Buckthorn (Rhamnus cathartica): Best Management Practices in Ontario”: https://www.ontarioinvasiveplants.ca/wp-content/uploads/2018/05/OIPC_BMP_Buckthorn_May282012_D61.pdf
Ontario Invasive Plant Council’s “European Buckthorn (Rhamnus cathartica) Best Management Practice Technical Document for Land Managers”: https://www.ontarioinvasiveplants.ca/wp-content/uploads/2017/05/OIPC_TechnicalBMP_Buckthorn_Apr282017_D5_WEB.pdf
- Ontario’s Invading Species Awareness Program. 2012. “Common Buckthorn (Rhamnus cathartica)”. Ontario Federation of Anglers and Hunters. Web. 14 August 2018. http://www.invadingspecies.com/common-buckthorn/
- Ontario Ministry of Natural Resources. 2012. “Common Buckthorn (Rhamnus cathartica)”. Web. 14 August 2018 . https://dr6j45jk9xcmk.cloudfront.net/documents/3192/stdprod-104385.pdf
- Anderson, Hayley. 2012. “Invasive Common (European) Buckthorn (Rhamnus cathartica): Best Management Practices in Ontario.” Ontario Invasive Plant Council, Peterborough, ON. Web. 14 August 2018. https://www.ontarioinvasiveplants.ca/wp-content/uploads/2018/05/OIPC_BMP_Buckthorn_May282012_D61.pdf