November Weed - Oriental Bittersweet
In her final weed article, Mary Anna Anderson of UNL Extension writes of a beautiful but invasive weed. It has been sold at nurseries and garden centers throughout the U.S. Unfortunately, it has some bad habits and outcompetes with our native plants. Thank you for sharing information with us, Mary Anna, and enjoy retirement!
Weed - Celastrus orbiculatus is also known as Oriental bittersweet, Asian or Asiatic bittersweet, climbing spindleberry, and round-leaved bittersweet.
Description: C. orbiculatus is a vine that can grow to 60 feet long with a stem diameter up to 5 inches. The stem bears blunt thorns. The leaves are alternate, glossy, roundish and nearly as wide as they are long, with a finely toothed margin. The plant grows in a wide variety of soils and moisture levels. It is dioecious (with separate male and female plants), however perfect flowers have been occasionally found on plants. The female flowers and fruits arise from the leaf axils. The male flowers bloom on the ends of the growing points. Our native or American bittersweet (Celastrus scandens) has male and female flowers at the end of the stems of their respective plants. Location of the flowers is the main way to tell the invasive Oriental bittersweet plant from our native bittersweet.
Where: Oriental bittersweet grows on forest edges, in deep forests, thickets, open fields, roadsides, fence rows, and beaches. It grows well in both low light and full sun. In contrast, the native bittersweet will not grow in full sun.
Propagation: Oriental bittersweet reproduces vegetatively from roots and root pieces. Injuring the roots encourages sprouting. It also reproduces from seed spread mostly by birds, and by people who collect the plant for dried arrangements and allow the seeds to fall to the ground. Seed requires stratification (a cold period) in the soil before it can germinate. The germination rate is 85%.
Poisoning: Celastrus orbiculatus is not known to be poisonous, unlike the true bittersweet Solanum dulcmara. However, the berries have been reported to cause intestinal upset and vomiting.
Historical: Brought to the U.S. from Asia in the 1860s, it was used for erosion control and as an ornamental. It is still found in temperate zones of Japan, Korea, and China (north of the Yangtze River), primarily in lowland slopes or thickets below 1,500 feet. Oriental bittersweet is known to have spread throughout the eastern two-thirds of the U.S., except Florida. The first reports of naturalized specimens were in Connecticut in 1916. By 1971 it was considered weedy in all of New England and most of the Atlantic Coast States. In 1974 it was reported to be naturalized in 21 of the 33 states where it had been cultivated.
What: C. orbiculatus is on the Nebraska noxious weed watch list. This means it is not known to be in Nebraska but poses a significant threat if introduced. Oriental bittersweet readily hybridizes with the native C. scandens. It can be difficult to identify the hybrids. According to the U.S. Forest Service, a bittersweet hybrid in Connecticut was found to have produced two types of pollen.
Pros: In autumn, bittersweet vines put on an eye-catching display of yellow foliage, and the deep yellow capsules burst to reveal red berries (arils) that look like jewels. The plants are dried to use in decorative arrangements. Birds, including blue jays, chickadees, European starlings, northern bobwhites, ring-necked pheasants, and wild turkeys eat the berries (and spread the seeds). Wildlife that feed on the plant include fox squirrels and eastern cottontails.
Medicinal: According to Plants for a Future, there are many medical uses: "A decoction of the roots and stems is used internally whilest the crushed fresh leaves are used for external applications. The plant is used in the treatment of paralysis, numbness of the four extremities, headache, toothache, spontaneous abscess formation, and snake bites. Many plants in this genus contain compounds of interest for their anti-tumor activity."
Cons: Oriental bittersweet is extremely invasive. It is outpacing the native bittersweet, which seems to have disappeared in some parts of the northeast U.S. C. orbiculatus takes over forested areas and kills in multiple ways. It wraps around trees and shrubs and strangles them. It will also cover the canopy of plants, shading them to the point of death. Oriental bittersweet can get so large and heavy that it can cause trees to be uprooted and fall over.
The U.S. Forest Service has a detailed website about studies of Oriental bittersweet in various states.