Flower:

Clusters of up to 7 stalked flowers (frequently 3), forming in the leaf axils of this year's side branches of older woody stems, occasionally also at the tip of a branch. Flowers are ¼ to 1/3 inch across with 5 green to yellowish petals and 5 green sepals. Male and female flowers are typically on separate plants, rarely on the same plant and rarely a plant will have perfect flowers (having both male and female parts). Male flowers have 5 stamens with creamy white tips (anthers); female flowers have a stout style with a 3-lobed stigma at the top. Flowers are on a slender, hairless stalk.

Leaves and stems:

Leaves are alternate, 2 to 5 inches long and 1½ to 3 inches inches wide, have rounded teeth around the edges, are smooth on the upper surface, and may have sparse hairs along the veins on the underside. The slender leaf stalk is about ¾ inch long.

Leaf shape is somewhat variable, nearly round to oval or may be broadest at the tip end. The tip is rounded, or with an abrupt sharp point, or with a short taper to a point. The base is rounded, slightly heart-shaped, or slightly tapering to the stalk. Woody branches are gray-brown to brown with scattered conspicuous white pores (lenticels); the trunk, which can be 4 inches in diameter, has more roughly textured bark. This vine has no tendrils; it twines around trees and other structures for support.

Fruit:

Fruit is round, about 1/3 inch across, initially green, the outer casing turning yellow in late summer then splits open to reveal a bright red, 3-sectioned berry-like fruit, each section containing 1 or 2 seeds.

Notes:

This, commonly known as Round-leaf Bittersweet or Oriental Bittersweet, is a Very Bad plant, brought into North America as an ornamental and escaped into the wild. It is a terrible pest plant in the eastern U.S. and was just getting started in Minnesota when we first published this in 2013. Now it's well established and spreading irrespective of its noxious weed status. It spreads by both seeds and rhizomes, suckering like mad and creating incredibly dense walls, blocking nearly all light from whatever used to grow beneath it. The vines wrap themselves around trees and can strangle them, or even bring them down from the sheer weight of its leafy arms.

Incredibly, it is still sold as nursery stock in some areas. It should be banned in the U.S., but there is too much money to be made selling “exotic” plants, so there really is no stopping it. In Minnesota it was initially listed as an Eradication species, meaning the MN Department of Agriculture (MDA) targeted it for extermination while it was still relatively few in number here. That was apparently a lost cause so it was downgraded to “prohibited control noxious weed”, which means it cannot be propagated or sold in the state and is supposed to be controlled to prevent spread, but I fear that is also a hopeless endeavor. Populations have been tracked on the Invasive Plant Atlas and EDDMaps.

When not flowering or fruiting, it is very difficult to distinguish from the native American Bittersweet (Celastrus scandens) but there are a number of differences to aid in a positive ID.

• When flowering or fruiting, C. orbiculatus has mostly small clusters in the leaf axils of a branch where C. scandens will have one large cluster at the end of a branch.
• C. orbiculatus flowers are typically greener with narrower petals than C. scandens.
• The male flowers of C. orbiculatus have creamy white anthers where those of C. scandens are distinctly yellow.
• The fruits of C. orbiculatus have a yellow casing, where fruits of C. scandens have an orange to red casing.
• Newer woody stems of C. orbiculatus have obvious white lenticels, where C. scandens lenticels are less conspicuous.
• C. orbiculatus leaves are generally rounder and proportionately broader than C. scandens , with C. scandens more finely serrated, but this is variable.
• In early spring when plants are just starting to leaf out, C. orbiculatus leaves are mostly flat or folded in half, opening like a book, where C. scandens will have the leaf edges rolled up like a scroll, though leaves developing later in the season may not be so easily distinguished.

The images on this page show many of these comparisons.

The two species are apparently capable of hybridizing, but whether this actually occurs in the wild is unknown and there is very little information available on this subject. Buyer beware: American Bittersweet is also available in the nursery trade and some vendors advertise selling it, but turns out to be Round-leaf Bittersweet instead. This isn't necessarily intentional, but just shows that those selling it can't always tell the difference, either. Know your source!