Our March Weed of the Month is Roundleaf bittersweet (Celastrus orbiculatus). Roundleaf bittersweet is a woody vine species that is originally native to several countries in Asia. It was introduced to North America as an attractive ornamental species because of its showy red fruits in the fall. The vines begin on the ground and eventually grow vertically up nearby trees. The leaves alternate along the vine, are round in shape, and have lightly toothed margins all throughout. The small, 5-petal flowers appear in the leaf axils (the space where the leaf stem meets the main stem) between May-June.

The behavior (and subsequent management strategies) of this vining plant is similar to Ivy (Hedera sp.), another problematic vining plant throughout the Northwest. Roundleaf bittersweet becomes problematic in forested areas because it grows so vigorously on trees that it effectively girdles them (stops the flow of nutrients from roots to canopy). It also mimics ivy behavior because the vines typically do not produce fruit until they grow vertically into tree canopies.

As of late winter 2026, this species has not been detected in Benton County, OR. However, it was detected in neighboring Clark County, WA as of late 2025. If you believe you have seen this species in Oregon, report it online to the Oregon Invasives Hotline.