Oriental bittersweet (Celastrus orbiculatus)
Oriental bittersweet is a deciduous, woody vine native to the regions of China, Korea, and Japan. It is extremely shade tolerant and grows in forests, woodland edges, grasslands, roadsides, and fencerows. It was brought to the United States in the mid 1800s as an ornamental plant and has since escaped and spread throughout the eastern US and Canada.
Oriental bittersweet grows by twining around shrubs and trees. It can grow up to a height of 18 m when tall trees are present. It has alternating glossy leaves that are rounded with finely toothed edges. The stems are light brown, with noticeable lenticels and have solid white piths. The roots of the plant have a characteristic orange colour. Oriental bittersweet is dioecious, meaning there are separate male and female plants. It blooms May to June, producing greenish yellow flowers in the leaf axils. Female plants produce round leathery seed pods that are green at first but turn a bright yellow or orange yellow in fall. The seed pods open to reveal a red fruit which contains three to six seeds. These seeds are then distributed by birds that eat the fruit.
Oriental bittersweet can easily overrun native vegetation, forming nearly pure stands. It can strangle shrubs and small trees and weaken or even kill mature trees by girdling the trunk and smothering the crown. Oriental bittersweet prolifically reproduces both by seed and spreading its underground roots which sprout new stems. Because of this, it is a major threat to any ecosystem it invades. There is also evidence that it can hybridize with the native American bittersweet (C. scandens), which could threaten to genetically eliminate this native species. The American bittersweet is distinguished by flowers clustering at the tips of its branches, while Oriental bittersweet has flower clusters along the leaf axils.
Oriental bittersweet can become a serious problem if not detected and removed early. It can be removed by pulling or digging provided the root is removed entirely. If the plant is female, it should be removed before it goes to seed. Larger vines are much more difficult to remove and often need to be cut and stump treated with a herbicide.
CVC is interested in any locations of Oriental bittersweet in our watershed. Contact us at 905-670-1615.