I live on the edge of zone 5 very close to zone 6. We have a creek that floods pretty regularly in the spring. A section is pretty much wetland and when it floods the plants are completely submerged. I usually forage for plants in the area. Mostly skunk cabbage, stinging nettles, and cattails grow in the really wet places. Trees that grow there are larch and willows. There are also wild raspberries but I think they are higher up on the hillside.
-Hollis