American bittersweet, Celastrus Scandens, is a native woody-stemmed perennial vine with short, softly ovalled, slightly toothed, often shiny leaves that taper to a point. Often confused with Bittersweet Nightshade Solanum dulcamara, or with Oriental Bittersweet, Celastrus orbiculata, an invasive, Asian variety which has rounder leaves and is starting to crowd out the native variety in many American forests.
For more about bittersweet and native plants for the Midwest, especially those that do well in shady and moist areas, see the "book" on this website, Gardening with Native Plants in Shady Evanston.