I get asked all the time about possibilities for sites that are not quite wetlands, but that are saturated in the winter time. Conventional wisdom holds that these places are too wet to grow food, but I know it can be done. Here are some plants that I have heard of and/or seen used on wet sites. Please feel free to add to it, or tell me what your experience has been with them.
Note: This is for sites where earthworks can’t be done for one reason or another, and the site has to be used as-is.
Pacific Crabapple (as a rootstock for other apples)
Willow (basketry, medicine, rooting hormone)
Quince (as rootstock for quince and other fruits)
I have seen people plant in mounds (berms) with some success, though even with plants on them these tend to erode over time. Building hugelbeds in the forest garden seems to wick away excess moisture and improve fertility.