Here is a link to the Mo. Botanical Garden Plant Finder: I input zone 4, clay soil, wet soil and got 3 pages of stuff to look at. Don’t know if any will be suitable.
http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plantfinder-results.aspx?zone=4&Clay=true&Wet=true&displayview=profile
that’s really cool