Does this look like an American (i.e. native) bittersweet vine? It is a volunteer growing in a shady area in my backyard, and I have not seen flowers or berries on it. It has a very strange trait: the leaves on the part of the vine that I touch while guiding it around a plant support temporarily wilt...not the entire vine, just the leaves I handle.
I think it may be 'a' bittersweet. Besides flower/ berry habit, check sites about leaf shape for telling that apart from Oriental.
If it volunteered, its very possible to be an Oriental.
Never heard of that wilt effect.
Thanks for your suggestions. The leaves and stems do look like the native variety. I hope it'll flower next spring so I'll know for sure. I do have a number of native plants in my yard, including American Holly, Virginia Creeper, Green Briar and grapes, so I'll hold out hope that it's the American variety!