Gardeners in North America either love bittersweet vines or hate them. Bittersweet plants can kill trees and are difficult to eradicate from your landscape. But during the fall season bittersweet vines put on a display few other plants can rival, as the deep yellow skin of their berries bursts to reveal an orange jewel within. And not to be outdone by the berry, bittersweet plant's fall foliage blankets its victims in yellow splendor. To grow bittersweet vines or not to grow bittersweet vines: truly a bittersweet decision for landscapers.
But exactly what plant are we talking about? There are two vines with yellow and orange berries commonly called "bittersweet." They look very much alike. One, an innocuous vine indigenous to North America with smooth stems, is Celastrus scandens, also called "American bittersweet" plant or "false bittersweet." The other, an exotic vine that is among North America's most invasive plants and whose stem bears blunt thorns, is Celastrus orbiculatus, or "oriental bittersweet" vine. Another way to distinguish between American bittersweet and oriental bittersweet is by discerning the location of their berries: the berries of American bittersweet plants appear at the tips of the vines only, while those of oriental bittersweet vines grow along the vine. But the biggest distinction between the two is in terms of their environmental impact. For while oriental bittersweet vines are considered an environmental menace by many, American bittersweet plant is becoming so rare in some areas that it is now a protected species. It is the oriental bittersweet vines that threaten to kill your trees; while American bittersweet plants are themselves threatened.
According to the USDA Natural Resources Conservation Service, American bittersweet plants occur naturally in the central and eastern U.S., except in Florida. Meanwhile, according to the U.S. National Park Service, oriental bittersweet vines are native to eastern Asia; they were introduced into the U.S. in the 1860s. Reporting on the spread of oriental bittersweet vines in the U.S., the Park Service says that they occur "from New York to North Carolina, and westward to Illinois."
In fact, the exotic oriental bittersweet vines have spread so successfully that they are beginning to displace their native rival. "There are several characteristics of C. orbiculatus that make it a better competitor than its native cousin," states Conservation New England. "Oriental Bittersweet Vine produces fruits that are a brighter shade of red, and also produces more of them, so that birds are more likely to disperse the seeds of C.orbiculatus than C. scandens. These seeds also have a higher rate of germination. C. orbiculatus is also better at photosynthesizing, with the ability to absorb light from a wider range of the spectrum (Dreyer 1985). The result is that the Asian invader has displaced the native plants right out of their habitat niche."
The powerfully invasive oriental bittersweet vines engulf other vegetation, slowly killing it. The germination of a bittersweet seed in the ground at the base of a tree seems harmless enough. Yet, it won't take long for the oriental bittersweet vine to make it to the tree's crown, a la Jack's beanstalk made famous in folklore. It can be difficult to imagine a vine killing a tree, but oriental bittersweet vines have slain many a giant. Capable of reaching four inches in diameter, oriental bittersweet vines wrap so tightly around their victims that the trees are strangled, in a process called girdling by arborists. Even when oriental bittersweet vines aren't strangling a plant, they envelop it in so much shadow that they rob the plant of the sunlight required for proper photosynthesis. Conservation New England reports that, in the case of smaller trees, uprooting can even occur, as the trees' root systems are unable to contend with the massive weight of entrenched vines.
But you may be wondering at this point, "If American bittersweet plant is also dubbed 'false bittersweet,' then is there a 'true bittersweet'?" The answer is, Yes, but the true bittersweet is not represented by the oriental bittersweet vines, either. To discuss the plant properly called "bittersweet," we'll have to introduce a third plant into the linguistic fray. For the true "bittersweet" is a plant markedly distinct from both oriental bittersweet vines and their rivals indigenous to North America. And, although its berries are poisonous, the true bittersweet, as we'll see on Page 2, has been used traditionally by herbalists as a medicine....
