It is easy to distinguish female plants of the species in the summer, fall and winter by the position of the flowers and fruit. Flowers and fruit are at the leaf axils on round leaf bittersweet and are only in terminal panicles on American bittersweet stems. Also, the fall fruit capsule color is yellow for round leaf bittersweet and orange for American bittersweet. It is more difficult to distinguish male plants because they do not set fruit. Flower position is still indicative. During the spring, leaf unrolling is also indicative. Conduplicate (folded in half lengthwise with the upper side inward) leaves are round leaf bittersweet and involute (inward curling) leaves are American bittersweet. Other potential characteristics such as leaf shape (round leaf bittersweet has rounder leaves) and fruit number per cluster are highly variable and indefinite.
Differentiating Round Leaf and American bittersweets
As of December 2022, the Minnesota Departments of Agriculture and Natural Resources and the University of Minnesota Extension discontinued the use of “oriental bittersweet” as a common name for Celastrus orbiculatus. Round leaf bittersweet is the new common name. The Minnesota Department of Agriculture is committed to phasing out the discontinued common name and adopting the new common name. Documents and other materials will be updated to educate the public about the name change.
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