The plant genus Celastrus, commonly known as bittersweet, is frequently encountered across North America. The continent hosts two primary species: the indigenous American Bittersweet (Celastrus scandens) and the exotic, highly aggressive Oriental Bittersweet (Celastrus orbiculatus). Understanding which vine you see is the first step in proper ecological management. The question of whether American Bittersweet is invasive stems from this common misidentification, making accurate distinction important for conservation.
The Core Distinction: American vs. Oriental Bittersweet
Correctly identifying the species relies on observing the arrangement of its flowers and fruits. American Bittersweet produces its clusters of flowers and subsequent berries only at the tips of its branches (terminal clusters). Oriental Bittersweet displays its smaller fruit clusters along the entire length of the stem, emerging from the leaf axils.
Leaves also offer a visual clue. Leaves of the native American vine tend to be more elongated, elliptic, or football-shaped, tapering to a distinct point. Oriental Bittersweet typically has leaves that are much broader and rounder, often nearly as wide as they are long, sometimes earning the nickname “round-leaved bittersweet.”
Growth habit reveals differences in aggression and size. American Bittersweet is a less vigorous climber, generally reaching lengths of up to 20 feet, and its bark is reddish-brown. Oriental Bittersweet is an aggressive, woody vine that can reach heights of 60 feet or more, with stems often growing to four inches in diameter. The invasive species has light brown bark with a white pith, though older stems may develop a red-brown, cracked texture.
The Native Status of American Bittersweet
American Bittersweet is not invasive; it is a native species to central and eastern North America. This vine is an established component of local ecosystems, found in habitats ranging from thickets and woodlands to stream banks. Its presence supports local wildlife, as its distinctive orange capsules open to reveal scarlet-coated seeds that are a food source for birds and small mammals throughout the winter.
Despite its native status, the American species faces significant challenges. Due to competition from the aggressive Oriental variety, C. scandens is considered uncommon or vulnerable in several northeastern states. Habitat loss also contributes to its decline, as the native vine is being displaced by its foreign counterpart.
The native species does not form the dense, damaging stands associated with the invasive variety. Its growth rate and maximum size are significantly less than the Oriental species, meaning it rarely causes severe damage to supporting trees. Its ecological role is that of a valuable native plant, which is why accurate identification is important before any removal efforts are initiated.
Understanding the Invasive Threat
Oriental Bittersweet is classified as invasive due to the aggressive mechanisms it uses to dominate native plant communities. The vine exhibits prolific seed production, with seeds dispersed widely by birds who consume the abundant fruits. This high reproductive rate allows it to rapidly colonize new areas, including roadsides and woodlands.
The primary threat to trees is girdling, caused by the vine’s twining growth pattern. As the woody vine wraps tightly around a host tree and increases in diameter, it constricts the flow of nutrients and water through the vascular system. This action can severely wound or kill large, mature trees.
Another destructive behavior is overtopping, where the vine quickly climbs into the forest canopy. It spreads out to form thick mats of foliage, blocking sunlight from reaching the host tree’s leaves. This smothers the tree, depleting its energy reserves and making it susceptible to disease.
The weight of the vine mass, especially when covered in ice or snow, adds mechanical stress to the host tree, increasing the likelihood of limb breakage during storms. Hybridization compounds the problem, as the Oriental species interbreeds with the native American species. This dilutes the genetic integrity of the native population, creating hybrid offspring that may inherit the invasive traits.
Management and Control
Control efforts should focus entirely on the invasive Oriental Bittersweet. For small, young plants, the most effective method is grubbing, which involves digging up the entire plant and removing all root portions. Any piece of root left in the soil can re-sprout, making thorough removal necessary.
For established, mature vines climbing trees, the recommended mechanical technique is the “window-cut” or “cut-stump” method. This involves making two cuts on the main vine: one at ground level and a second cut a few feet higher, removing the section in between. The aerial portion is left hanging to die, as pulling it down can severely damage the host tree.
The rooted stump must be chemically treated immediately after cutting to prevent re-sprouting. A concentrated systemic herbicide, such as glyphosate or triclopyr, should be applied directly to the fresh-cut surface. This allows the chemical to be absorbed and translocated down to the root system, killing the entire plant.
Proper disposal of the removed plant material is the final step to prevent further spread. All parts of the vine, especially those bearing fruit, should be bagged and disposed of in the trash, not composted. This precaution ensures that the seeds, which are readily dispersed by birds, do not contribute to new infestations.