Bittersweet
By Carol Gracie

The brightly colored fruits of bittersweet are a common decorative accent on holiday tables and doorways in autumn. Although commonly called berries, the fruits are actually capsules. When the fruits mature in fall—generally after the first frost, the yellow-orange capsules split into three valves revealing three bright red fleshy arils, each surrounding 1-2 small seeds. Arils are fleshy outgrowths of the structure that attaches the seed to the fruit wall. This colorful display of contrasting colors serves to attract birds, and perhaps small mammals, that eat the oil-rich arils and later excrete the seeds. Thus, the plant has evolved an effective method of ensuring dispersal for its seeds. The fruits are generally not a preferred food of birds in fall, but rather remain on the plant into winter when they serve as a welcome resource for bluebirds, chickadees, starlings, and other birds.

In the Northeast two species of bittersweet may be encountered, one quite rare, the other all too common. It’s important to learn to distinguish the two species so that one knows which to encourage and which to eradicate. Our native American bittersweet (Celastrus scandens) was once a common element of the local landscape. It is now rare in our area due both to over-collecting for decorative purposes and competition from its alien relative, Oriental (Asiatic) bittersweet (Celastrus orbiculata—note the recent correction in name from the former erroneous C. orbiculatus).

American bittersweet is native in 39 states and five Canadian provinces (but now extirpated in New Brunswick). It is a woody, deciduous vine that climbs by twining around any suitable object it contacts or around itself, thus the species name, scandens, meaning climbing. The plants are mostly dioecious, that is they have either male or female flowers. The most reliable way to distinguish our native species from the introduced one is by the location of the flowers and fruits on female plants. In American bittersweet, the clusters of flowers and resulting fruits occur at the tips of the branches. Oriental bittersweet produces its smaller clusters of flowers and fruits along the stems where the leaves are attached. This arrangement results in a greater number of fruits being produced. Also, the capsules of C. scandens are usually more orange than those of C. orbiculata. Other than the difference in the location of flowers and fruits, the plants are much the same in appearance with brownish stems dotted with small, light spots (the lenticels) and shiny, green, slightly toothed leaves that become yellow in late fall. The leaves are variable in size and shape, but those of American bittersweet are generally longer than broad while those of Oriental bittersweet are more rounded in outline giving rise to the species name, orbiculata. Both produce inconspicuous, green, five-petaled flowers in spring. Bees are the most frequent visitors and the most likely pollinators. In addition to being grown for its attractive appearance, C. scandens was used medicinally by Native Americans and early settlers, and its stems were used in the production of rope and weaving materials. If you are fortunate enough to locate a site with American bittersweet, it should be protected and encouraged to grow by the removal of competing vines. New York State DEC includes C. scandens on its list of Protected Plants, categorizing it as “exploitably vulnerable.” It is on their review list to determine if it should be officially designated as rare in the state. The picking or removal of any species on the Protected Plants list growing on public property is in violation of state law and subject to penalty. On private property, permission of the owner must be obtained.

Oriental bittersweet was introduced into the U.S. in the second half of the 19^th century, both for its ornamental beauty and for its effectiveness in controlling erosion on roadsides. It is native to Korea, Japan, and parts of China. It spreads aggressively, not only by seed-dispersal, but also vegetatively through root-suckering. Broken stems and pieces of the bright orange roots left underground quickly resprout. By the second decade of the 20^th century, Oriental bittersweet was already noted to be naturalized in several states. It’s now found in 25 states from Maine to South Carolina and west to Montana. Twenty-two of those states report it as an invasive.

Bittersweet can kill plants on which it grows by girdling them as it twines tightly around the trunks such that the vascular tissue of the host can no longer transport water and nutrients. If the vines are killed or removed, their former host trees can often by recognized by the spiraling scars on their trunks. Bittersweet may also kill its hosts by over-shadowing them so that they can’t effectively photosynthesize. Masses of vines in the canopy of a tree may cause the tree to become top-heavy and, thus, more prone to being toppled by wind.

Studies have shown that Oriental bittersweet can absorb light in a wider range of the spectrum than American bittersweet and is, therefore, more efficient in photosynthesizing. In addition, it has a much higher germination rate (70% vs. 20% mean rate) than its native counterpart. Although Oriental bittersweet is found most often on the edges of woods with plenty of sunlight available, it can tolerate shade and is therefore adaptable to a variety of ecological conditions.

This alien invader is difficult to eradicate. It’s best to manually remove all traces of it as soon as it’s noticed. Broken off pieces of the underground portions must be dug up and discarded where they won’t be able to regrow. In the case of massive invasions, the use of herbicides may be necessary. When discarding decorative arrangements containing Oriental bittersweet, don’t add them to the compost pile or otherwise dispose of them where the seeds could germinate. This serves to perpetuate the problem.

See Carol Gracie's Scenes of the Seasons - Autumn

Photos Courtesy of and Copyright © by Carol Gracie
cgracie@optonline.net

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