When wandering through the Arb, you may encounter a pop of color in the gray winter woods: a bush spangled with bright red-orange berries. Look a little closer, and you’ll notice that those berries aren’t attached to a bush at all, but a vine! This is the American Bittersweet, a native species of vine that can grow thirty feet long or more, using neighboring trees as a trellis. Most of the time this isn’t much of an issue for adult trees, but sometimes it may kill saplings that are constricted as they grow. The bittersweet is well-adapted to frigid Minnesota winters; in fact, it needs them to survive – its seeds require months of cold temperatures in order to break their dormancy and successfully germinate in the spring. Without this cold stratification period, the seeds may not sprout at all.
The bittersweet’s beautifully colorful fruits are small, only about half an inch wide, their three-piece casings opening to reveal the bright red fruits beneath in the fall. These persist throughout the winter, providing an important food source for many birds, squirrels and foxes when the ground is covered in snow. They’re poisonous to humans though, so don’t be tempted to nibble one! Instead, many florists will use bittersweet branches in dry flower arrangements and winter décor, or as landscaping accents in gardens.
The bittersweet’s beauty in residential landscaping has also led to the introduction of its decidedly less-friendly cousin from overseas, the invasive Round-leaf Bittersweet. This species creates dense walls of foliage in the summer that block sunlight from reaching anything growing beneath it, and it’s known to strangle trees of all ages. It can even uproot some trees due to the strain of its sheer weight. Unfortunately these two bittersweets can be devilishly hard to tell apart, especially in winter, which can make eradication of the Round-leaf Bittersweet particularly difficult. The easiest way to tell at this time of year is by looking at the fruiting pattern: American Bittersweets usually have fruits in one big cluster at the end of each branch, while Round-leaf Bittersweets has many smaller clusters all along the branches.
Next time you’re out in the Arb, keep an eye out for the bittersweet’s fiery berries, brightening the chilly winter woods – and see if you can tell whether it’s native or invasive!
For more information, check out these great articles from Minnesota Wildflowers:
American Bittersweet (https://www.minnesotawildflowers.info/shrub/american-bittersweet)
Round-leaf Bittersweet (https://www.minnesotawildflowers.info/shrub/round-leaf-bittersweet)
- Stephanie Holmes ‘28, for the Cole Student Naturalists
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