Differentiating Round Leaf and American Bittersweets

Round leaf bittersweet, Celastrus orbiculatus, is a woody vine native to China, Korea and Japan. It was introduced to North America in the mid-1860's as an ornamental. Round leaf bittersweet has since spread throughout the temperate eastern United States and Canada. In 2010, round leaf bittersweet was added to Minnesota's Noxious Weed List. There is a closely related vine native to North America named American bittersweet, C. scandens. They grow in the same habitats. Here is some guidance to help distinguish the species.

Round leaf bittersweet fruits are red with yellow capsules surrounding the fruit. American bittersweet fruits are red with an orange capsule surrounding the fruit.

Round leaf bittersweet fruits occur along the entire stem at leaf axils.

American bittersweet fruits are in clusters at the terminal ends of stems.

Round leaf bittersweet flowers are arranged in clusters along the stem at the leaf axils. American bittersweet flowers are arranged in clusters at the terminal stem.

Each flower has 5 petals and 5 sepals. Female flowers have a centered ovule. Pollen on round leaf bittersweet is white and on American bittersweet is yellow.

Round leaf bittersweet has a rounded egg shape leaf. According to  USGS , Celastrus orbiculatus has a length to width ratio less than 1.4 and a leaf tip less of 0.3 cm. American bittersweet has a long pointed leaf. According to  USGS , Celastrus scandens has a length to width ratio greater than 2.0 and a leaf tip greater than 1.5 cm.

Round leaf bittersweet buds are dome shaped. American bittersweet buds are pyramidal. The buds are very small so magnification is needed to see them.

During the spring, round leaf bittersweet leaves unfurl folded in half lengthwise with the upper side inward ( conduplicately ). American bittersweet leaves unfurl inward curling ( involutely ).

Round leaf bittersweet bark is highly textured, light gray to light brown. American bittersweet bark is smoother and grey to brown.

Round leaf bittersweet vines wrap tightly around native vegetation climbing up the tree in a serpentine pattern. The tight wrapping vine girdles the host it is on cutting off nutrient flow. Vines can reach a diameter of 10 inches.

American bittersweet vines are less aggressive than round leaf bittersweets. American bittersweet vines wrap loosely around native vegetation. Vines can reach a diameter of 2.5 inches.

To report infestations of round leaf bittersweet, please do the following:

•  If it is possible, take digital photos of the whole plant, vine, flowers, and berries that can be emailed for identification. Infestations can be reported directly to  EDDMapS  using the website or free EDDMapS App available at the Google Play and Apple App stores.

To learn more about the MDA’s  Noxious and Invasive Weed Program  and the Noxious Weed Law and Lists, please visit:  www.mda.state.mn.us/weedcontrol