from Maine Wetlands and Their Boundaries: A Guide For Code Enforcement Officers, by Ralph W. Tiner
Shrub swamps are dominated by woody vegetation less than 20 ft tall. They are seasonally flooded and often saturated near the surface when not flooded. Common species include buttonbush, broad-leaved meadowsweet, steeplebush, speckled alder, sweet gale, mountain holly, northern arrowhead, maleberry, red osier dogwood, silky dogwood, highbush blueberry, willows, and common winterberry. Herbs include skunk cabbage, false hellebore, flat-topped aster, New York aster, marsh fern, cinnamon fern, and sensitive fern. Some shrub swamps are dominated by saplings of trees such as red maple, black gum, and larch.