Answer: You have asked an interesting question. There is a type of bittersweet native to North America, Celastrus scandens. This plant can be found in the wild twining and clumping its way along, occasionally I suppose outcompeting, smothering or strangling plants in its path although it draws its sustenanace through its roots rather than from other plants. There is another type of bittersweet, Celastrus orbiculata, or Chinese Bittersweet. This plant is similar to the native bittersweet but even more rampant. It has escaped from cultivation and has "naturalized" through much of the Northeastern US. As such it is an "escaped exotic" or, in other words, native plant specialists would call it a nasty weed. I'm not sure that's what you meant by parasite, but some certainly consider it to be a pest.
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