Friday, February 27, 2015

Invasive Species Awareness Week: Oriental Bittersweet

Oriental bittersweet vine girdling a tree. Photo by Angela Isackson.
 Post contributed by Samantha House, seasonal natural resources technician:

Oriental bittersweet (Celastrus orbiculatus) is not commonly known, but it is a noxious weed according to the Minnesota Department of Natural Resources. This troublesome vine should be on every Minnesotan’s ‘watch list’. Native to Asia, this plant easily overtakes forested areas by wrapping and twisting around trees ultimately girdling and killing them. In addition to smothering trees, Oriental bittersweet is capable of pulling down trees in its attempt to accrue sunlight. The vine has been recorded to grow up to fourteen inches in only a couple of months  – you can imagine how quickly a young infestation can take over an area if left untouched.  

Oriental bittersweet fruit. Photo by Angela Isackson.
One should note this deadly vine has a native counterpart, American bittersweet. The easiest way to identify Oriental versus American bittersweet is the fruit positioning on female plants. Oriental bittersweet has axillary fruit – meaning, the flowering/fruiting occurs at the leaf axils and along the stem; whereas American bittersweet has terminal fruit – fruiting occurs near the end of the stem. Furthermore, Oriental bittersweet generally has yellow fruit capsules versus American’s bright orange capsules. Some sources claim that if no fruit is present (i.e. a male plant) one can differentiate native/nonnative based on Oriental bittersweet’s rounder leaf shape, but this is not always the case. Often, this invasive plant can have leaves that closely resemble the native’s leaf structure and vice versa because the two species hybridize in nature. If in doubt, watch the plant over a period of time. American bittersweet seems to grow slower and does not have a malicious intent. Whereas, Oriental bittersweet will quickly cover an area with vines and tightly girdle trees. 

Knowing how to properly identify Oriental bittersweet is imperative if we are to properly eradicate the invasive. Though the seed is commonly spread by birds, humans play a part as well. This invasive vine is frequently used as ornamental pieces for their bright colored fruits. Some plant distributors have even mislabeled Oriental bittersweet as American.

Even though Oriental bittersweet is a high threat to Minnesota’s forests, its current distribution is limited – the silver lining. There is only one known infestation on Saint Paul Parks and Recreation land to date. Hence, if people are on the lookout for this smothering killer and take the proper steps to control it, we can realistically stop this invasive in its tracks before it becomes too late. Remember early detection and rapid response makes all the difference when it comes to invasive species!

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Test your knowledge of Oriental bittersweet and many other invasive species: