The Strangling Stranger

The bittersweet vine turns out to be one of those plants that you would like to love, but really shouldn’t. The native species Celastrus scandens has been declining in abundance for many years, and it is in danger of being replaced by an introduced foundation plant called C. orbiculatus.

American bittersweet in natural habitat

The native, which is sometimes known as “false bittersweet” to distinguish it from a nightshade (Solanus dulcamara) that also has red berries, is associated with riparian (riverside) habitats. Both the false and the true bittersweets are poisonous to humans if eaten.

Articles in the popular press have attributed the decline of the native to greater hardiness of the invasive species, which produces more berries, more often and are even a brighter shade of red than those of C. scandens. All of these factors make it more likely to be eaten by birds and dispersed to new locations.

Once C. orbiculatus has been transported from the managed to the unmanaged landscape it out-competes the North American species through its ability to absorb a broader spectrum of light and photosynthesize more effectively, and – in the final insult – to cross pollinate with the native, producing fertile hybrids that dissipate the gene pool of C. scandens.

The two species (in their unhybridized form) can be told apart by the presence of small thorns on the stem of the introduced taxon. They are not sharp and are distributed at wide intervals along the vine. The leaves of C. scandens and C. orbiculatus are similar, but in addition to having brighter red berries, the Asian vine carries fruit along its entire length, while the American vine has berries only at the ends of the branches.

Asian bittersweet with axial flowers (eventually berries)

Both bittersweet vines twine around whatever they are growing on. Eventually, like most woody twining vines, they will strangle and kill their host.

In our meadow garden, which is now five years old, bittersweet (the exotic) appeared two years ago. This year the plants have grown two or three feet, twining around the nearest herbaceous forb (which in most cases is a goldenrod plant in this meadow). Since I scythe the entire area and then mow it each November, nearly all the growth of these fast growing vines is accomplished in one growing season.

The extraordinary amount of rain that we received in April and May, followed by the record-breaking heat in June and July, has caused the goldenrod to stand taller this year than in any previous year. The goldenrod is the only forb that is not cropped by the deer, so it has grown unhindered and some species are now over five feet tall. The bittersweet at one location as actually climbed nearly to the top of the goldenrod and then started to grow laterally across the “canopy.”

Fast growing vine in a meadow garden

According to one source, C. orbiculatus was first planted in the New York Botanical Garden in 1897. It has spread throughout the New York City area from there by natural dispersal, but it is present across the northeastern United States because it has become a very popular ornamental.

The berries are undeniably beautiful and the rate of growth insures that the homeowner will have an impressive amount of vegetation covering an arbor, pergola or other structure in no time at all. The berries remain on the plant through the winter providing a welcome spray of color when there are few other natural sources of it.

Wreaths made out of bittersweet are a popular autumn and winter decorative item. They are commonly hung on front doors, over mantles, or wrapped around table centerpieces. The Mother Earth News (“the guide to living wisely”) surprised me by giving its readers instructions as to how to harvest bittersweet. This lengthy article included no admonition to harvest in a sustainable manner or to “forage” only where you had permission to do so (i.e., not in state parks). Oddly, it was a penny-pinching site that counseled the reader to harvest vines from their own gardens.

Although I didn’t find reference to over-harvesting as a contributing factor to the decline of native bittersweet, this is often the case with other plants that are used either in the ornament-making trade or in the herbal medicine business. So if you decide to make a wreath from bittersweet, learn to distinguish the Asian from the North American species, use the former, and rip the rest of the vine out of the ground.