Hey Suzie...If you're looking to go with another tree, I would go for a weeping willow (Salix bablylonica) or a red twig dogwood (Cornus sericea). You mention that this will be under a crabapple tree, which leads me to believe that a tree or shrub would likely not go that well in this location. You could also try Iris pseudacorus...aka Lily of the Kings. Actually there are a number of Irises that do fine with wet soil: Iris ensata, Iris siberica, Iris setosa. There are also a number of ferns that do just fine in wet soils: Dryopteris erythrosora, Athyrium niponicum, Polystichum minutum. I hope this is helpful. Cheers...Dr. Robby