On a walk in the woods or in a decorative autumn-themed wreath, you may spot a bunch of bright orange berries popping out of yellow seed capsules.
“If you do, that’s bad news,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “Those berries are from Oriental bittersweet, which is a very serious invasive plant. It’s so destructive in forests that it’s illegal to sell the plant or the berries in Illinois.”
Oriental bittersweet (Celastrus orbiculatus) is an aggressive, twining woody vine that winds around the trunk or branch of a tree like a boa constrictor. As it matures, it can climb right up to the top of a tree. The bittersweet’s thick foliage outcompetes and shades out native plants below.
The vine’s weight can pull down tree branches. Eventually, the bittersweet woody trunk can get so thick that it squeezes and girdles the tree, choking off the life-giving layer of water-conducting cells beneath the bark.
Oriental bittersweet is easily spread by birds that eat its abundant autumn berries. “Unfortunately, it’s also been spread by people who like the colorful berries in fall-themed décor,” Yiesla said.
Even though the plant is classified as an exotic weed in Illinois and can’t legally be sold, the berries still turn up occasionally in gift items or are sold at roadside stands. “If you come across them, don’t put them in your compost,” she said. “The seeds might survive and sprout. Instead, dispose of the berries in the trash.”
If you have a twining vine with orange berries climbing a tree on your property, get a firm identification before you take any action. Oriental bittersweet, which is native to China and Japan, is easily confused with American bittersweet (Celastrus scandens), a native plant that is not invasive.
Both plants are woody vines with similar leaves, so they are most easily distinguished by their autumn berries or their spring flowers. Oriental bittersweet has many small white spring flowers and later autumn berries that are distributed all along the vine. In American bittersweet, both the fruits and the flowers occur only in small bunches at the ends of twigs, and there are far fewer of them.
Oriental bittersweet has yellow three-lobed seed capsules that split open to expose the red-orange berries. In American bittersweet, the seed capsules are orange, similar in color to the berries
If you have confirmed that a vine is Oriental bittersweet, use pruners, loppers or a saw to sever the vine’s trunk about a foot above the ground. Then treat the cut stump with an herbicide to prevent it from resprouting. Consult the Plant Clinic (mortonarb.org/plant-clinic) for help identifying the plant and for advice on choosing the right chemical and applying it safely.
“Don’t try to pull down the vine from the tree,” Yiesla said. “It can be very heavy and can be dangerous when it falls, and you might break the tree’s branches.” Instead, just leave the cut vine in place until it dries out and dies. Eventually, the dead vinewood will crack and fall away.
American bittersweet is hardy and native to the Chicago area and it is sometimes grown in gardens. Both male and female plants are needed to get fruit.
The vine can be grown on a strong trellis, arbor or fence. “It will grow to be a big, heavy plant, so be sure you have a sturdy support,” Yiesla said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
