Round leaf bittersweet

Round leaf bittersweet has been observed throughout the U.S. and Canadian portions of the Great Lakes Basin. It is reported in every U.S. state east of the Mississippi River with the exception of Florida and is common in the Midwest, New England, and the Mid-Atlantic. USDA reports Asian bittersweet as being hardy to a minimum temperature of -38^oF (Zone 3a). Particularly dense populations of round leaf bittersweet can be expected in areas where the species has been or still is popular as an ornamental landscape plant.

Additional invasive species distribution data for specific Great Lakes jurisdictions are available via:

• Midwest Invasive Species Information Network (Michigan)
• iMapInvasives (New York and Pennsylvania)
• EDDMapS Ontario

Seed is spread over distance by birds. Humans also contribute to its spread by planting mislabeled American bittersweet (Zaya et al. 2017) and using fruiting branches in dried flower arrangements or wreaths displayed or composted outside. 

Round leaf bittersweet occurs most frequently in forest edges, open woodlands, fields, hedgerows, coastal areas, and disturbed lands. However, its tolerance of shade allows it to invade interior forest areas too.

Round leaf bittersweet outcompetes native species by growing up and over native vegetation, blocking access to light, girdling trees, and making them more susceptible to ice and storm damage. It can establish large populations relatively quickly due to its high seed production and root suckering.

Ecologists are also concerned by round leaf bittersweet’s ability to hybridize with American bittersweet, diluting the native species gene pool. Zaya et al. (2021) found that where round leaf bittersweet and American bittersweet occur in the same habitat, it is common for asymmetrical hybridization to occur. This means that many female flowers of American bittersweet are fertilized by pollen from round leaf bittersweet resulting in hybrid seeds, while very few female flowers of round leaf bittersweet are fertilized by pollen from the native species. In a greenhouse setting, hybrid plants have demonstrated vigorous growth on par with the invasive parent (Pooler et al. 2002), though mature hybrid plants are not common in the wild and have very low fecundity (Zaya et al. 2015). Over time, it is feared reproductive interference and competition for resources with round leaf bittersweet will lead to further declines in American bittersweet populations.

Round leaf bittersweet has historically been valued as an ornamental plant due to its climbing habit, large quantity of bright fruit in winter, and low maintenance requirements. Stems with fruits are also sold as components of dried flower arrangements or winter wreaths. Round leaf bittersweet was also planted extensively for highway landscaping, wildlife forage, and erosion control. Although invasive species regulations in many states in the U.S. have diminished its popularity, retailers – particularly online retailers – often sell the invasive species mislabeled as the native American bittersweet (Zaya et al. 2017). 

None. round leaf bittersweet is dioecious and male cultivars do not produce fruit. However, they can still pollinate female round leaf bittersweet and American bittersweet plants.

Please see our Landscape Alternatives pages for more information about how the WIGL Collaborative selected alternatives.

~ = trait is somewhat present but not as pronounced as in check-marked examples

^a round leaf bittersweet is often mislabeled as its native cousin and sold by nurseries. If purchasing American bittersweet, it is very important to seek a reputable nursery (preferably one that specializes in woody and/or native plants) and ask questions to confirm it is, in fact, native bittersweet.
^b This cultivar is capable of self-pollination for fruit production unlike most other bittersweet varieties.
^c Trumpet honeysuckle fruit are colorful, but may not last into winter.
^d Virginia creeper and climbing hydrangea are clinging vines; they do best on solid surfaces like walls and wooden fences.

Green = native to all or part of the Great Lakes Basin
Yellow = native to North America but not to the Great Lakes
Blue = not native but not invasive

The WIGL Collaborative’s decision trees are designed to help site users, who are perhaps newly discovering that plants that are part of their home landscaping are invasive, prioritize which species should be removed first based on risk to the surrounding environment, economy, and occasionally, to human health. In a perfect world, everybody would remove all invasive plants from their landscaping right away, but in reality, removing mature woody plants involve a hefty investment of time and/or money. These diagrams can help people with multiple woody invasives in their landscaping prioritize to get the most benefit for their efforts.

To learn more about the methodology and information used to develop the decision trees and for helpful hints on how to answer the questions, please see the full report here (PDF).

The following is a brief overview of management techniques shown to be effective on round leaf bittersweet. For more detailed information on how to use these techniques, please visit our Management and Control page. For technical assistance on managing woody invasive species, please get in touch with a local cooperative invasive species management group.

Timing and spread concerns: Early detection is an advantage in managing any invasive species. Whenever possible, individual plants should be controlled before they are able to fruit in order to prevent spread. If control is undertaken after plants have fruited, it is best not to remove the plants from the site to avoid spreading seed. 

Physical control: Round leaf bittersweet plants can be pulled or dug up as long as the roots are completely removed. However, removal of a large root system can be difficult. Incomplete removal leads to extensive regrowth, which can result an overall increase in the population (Fryer 2011). Due to these concerns, physical removal is not recommended for large or established populations. Mowing of low-growing plants can be effective but only when the mower is set low enough to completely defoliate the plants and is repeated every two weeks during the growing season. A prescribed fire regime can kill seedlings and prevent seeds from germinating; land managers have had success in controlling seedling and small bittersweet stems (<1/8” diameter) with repeated annual prescribed fire in spring (Midwest Invasive Plant Network). However, prescribed fire is not recommended for established bittersweet populations as it tends to trigger extensive regrowth and suckering in mature plants, making infestations worse. If pursuing a combined approach as described below, cutting or mowing is more effective than burning as preparation for herbicide treatment (Pavlovic et al. 2016). 

Chemical control and combined approaches: Foliar, cut stump, and stem injection herbicide treatments are effective. Foliar spray may be the most feasible control method for a dense infestation of vines that have not climbed into desirable trees that would be damaged by herbicide. It is effective when plants are actively growing and fully leafed out. It is often most effective when combined with cutting or mowing with foliar herbicide applied to the resulting regrowth later in the season. Cut stump and stem injection treatments can be applied year-round outside of early spring and are also effective. In all cases, herbicide should be selected carefully based on site conditions, and label directions read and followed carefully. 

With any treatment, it will be necessary to monitor for and treat regrowth and new seedlings in subsequent years.

Management Resources

• Michigan Natural Features Inventory
• Midwest Invasive Plant Network Control Database
• U.S. Department of Agriculture, Natural Resources Conservation Service
• University of Wisconsin Cooperative Extension

• Fryer, J.L. 2011. Celastrus orbiculatus. In: Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. 10/23/19.
• Hilty, J. 2017. Oriental bittersweet. In: Illinois Wildflowers. 10/23/2019. 
• Midwest Invasive Plant Network. Invasive Plant Control Database. Oriental bittersweet case study. 10/23/19.
• Pavlovic, NB, Leicht-Young, SA, and Grundel, R. 2016. Oriental bittersweet (Celastrus orbiculatus): Spreading by fire. Forest Ecology and Management 364: 183–194.
• Pooler, MR, Dix, RL, and J Feely. 2002. Interspecific hybridizations between the native bittersweet, Celastrus scandens, and the introduced invasive species, C. orbiculatus. Southeastern Naturalist 1(1): 69-77.
• Sarver, M, Treher, A, Wilson, L, Naczi, R and FB Kuehn. 2008. Oriental bittersweet and American bittersweet. In: Mistaken Identity? Invasive Plants and Their Native Look-alikes. Delaware Department of Agriculture. 24-25. 
• Zaya, D.N., Leicht-Young, S.A., Pavlovic, N.B., Ashley, M.V. 2021. Heterospecific pollination by an invasive congener threatens the native American bittersweet, Celastrus scandens. PLOS One.
• Zaya, D, Leicht-Young, S, Pavlovic, N, Hetrea, C, & M Ashley. 2017. Mislabeling of an invasive vine (Celastrus orbiculatus) as a native congener (C. scandens) in horticulture. Invasive Plant Science and Management 10(4):313-321.
• Zaya, D.N., Leicht-Young, S.A., Pavlovic, N.B., Ashley, M.V. 2015. Genetic characterization of hybridization between native and invasive bittersweet vines (Celastrus spp.). Biological Invasions 17: 2975–2988.