Oriental bittersweet, an aggressive invader of woodlands, has become naturalized across northeastern Illinois.
Good Natured: Oriental Bittersweet
November 26, 2021
If you’ve been a Good Natured reader for any length of time, you’ve likely noticed that wildlife columns outnumber plant columns by at least two to one. With good reason! I’m just not very good with plants. Sure, I can point out our more notable natives, and I can lament non-native buckthorn, honeysuckle and garlic mustard til the cows come home. But for the most part I feel better leaving the commentary on our local flora to bona fide botanists and gardening enthusiasts.
However, every once in a while, a plant-related issue pops up that even I can’t ignore. Sometimes the topic is timely, sometimes it’s controversial. This week, though, it’s bittersweet.
Oriental bittersweet, that is: Celastrus orbiculatus.
A common component in holiday floral arrangements, this Asian vine with colorful berries is popping up across northeastern Illinois-not just in decorative swags and centerpieces, but also our yards, parks and natural areas. Like a distant relative who came for Thanksgiving dinner and now is camped out on your sofa, Oriental bittersweet is a guest that will not leave.
Although it resembles its native counterpart American bittersweet, C. scandens, Oriental bittersweet differs in many subtle but significant ways. For one, its berries grow from the leaf axils of the vine and are strung out along the stems; the fruit of American bittersweet, by contrast, grows only at the ends of its branches. (Easy ways to remember these differences, courtesy of the Minnesota Department of Agriculture and UMN Extension: “Strung out is bad,” and “Save the best for last.”)
Further, Oriental bittersweet fruit is surrounded by yellow seed capsules that pop open when ripe, while American bittersweet capsules are orange. (Another memory-helper: “Yell when you see Yellow; Orange is Okay.”)
But probably the biggest differences between these two vines are their growing habits. American bittersweet grows vigorously, yet behaves. It doesn’t blanket its surrounding landscape and smother everything in sight.
Oriental bittersweet, by contrast, has the capacity to strangle every tree and shrub it encounters. Its twisting vines can reach more than 60 feet in length, with additional shoots popping up as the roots spread. Allowed to grow unchecked, the plant can engulf a woodland canopy and shade out the trees and herbaceous plants below. What’s more, its weight, when accompanied by winter’s snow and ice, can cause branches to break and trunks to snap.
It’s a reckless beast, for sure. But how did it get here?
As is so often the case with introduced species, the very qualities that make Oriental bittersweet such a pernicious invader are the same traits that once made it attractive to gardeners here in the New World. Introduced as an ornamental in the mid-1800s, C. orbiculatus thrives in a variety of soils and growing conditions and produces prodigious quantities of fruit.
That fruit, which admittedly is kinda pretty, is really the root of the problem. Birds feed on the berries and then inadvertently distribute the seeds, which then germinate and start to grow.
Besides wildlife, humans are also to blame, since so many of us have purchased and transported the vines. Even though several states now regulate the sale of Oriental bittersweet (Illinois banned its sale in 2015) it’s not hard to find vines for sale on eBay.
Perhaps more distressing is the finding that vendors frequently mislabel their bittersweet stock. In 2017, Illinois Natural History Survey plant ecologist David Zaya and his colleagues published research showing that seven of 11 vendors in Nebraska, Missouri, Indiana and, yes, Illinois, were selling plants tagged as American bittersweet but in fact were the Oriental species.
This time of year, lots of folks are decking their halls, not just with boughs of holly but also with vines of bittersweet. Before you hang that wreath or garland with the abundant colorful berries, do yourself, your neighbors and your environment a big favor and double check your “decks.”
If your arrangement contains fruits even remotely resembling those in the accompanying photo, please don’t hang it up outside. More than a few of those berries are sure to drop into the soil, where a new vine will then result.
Use care when dismantling your decorations too. When it’s time for the trimmings come down, be sure to bag all the bittersweet and tie it up tight before tossing it in the trash. Don’t gamble that its seeds won’t survive in a compost bin; they’re tough, and likely will.
Burning the vines might be an even better disposal option, provided you watch to see every last berry go up in flames. They were pretty, for sure, but they need to become a bittersweet memory.
Pam Otto is the outreach ambassador for the St. Charles Park District. She can be reached at 630-513-4346 or email@example.com.