from Maine Wetlands and Their Boundaries: A Guide For Code Enforcement Officers, by Ralph W. Tiner
Fens are mineral-rich peatlands developed in areas of groundwater discharge and along rivers and streams. The avaliability of minerals creates opportunities for many wetland plants to grow. Larch and northern white ceder dominate wooded fens with red maple, black spruce, black chokeberry, sweet gale, blue flag, skunk cabbage, and rarely bog birch also present. Herbaceous fens are dominated by sedges, cottongrasses, white beak-rush, peat mosses, and liverworts.
Bogs are permanently sturated nutrient-poor peatlands dominated by heath or ericaeous shrubs (shrub bogs) and/or evergreen trees (forested bogs) growing in peat moss. They may on rare occasions be inundated. They are found in isolated depressions (kettles) and sometimes extend up adjacent slopes. They also occur behind narrow fens along rivers, streams, and lakes. Characteristic shrub bog species include leatherleaf, sheep laurel, bog laurel, bog rosemary, labrador tea, sweet gale, mountain holly, rhodora, black huckleberry, dwarf huckleberry, cranberries, and black chokeberry. Along the coast in Downeast Maine, black crowberry and baked appleberry may be locally dominant with tufted bulrush. Bog herbs include pitcher-plant, grass pink, rose pogonia, dragon's mouth, white-fringed orchid, sundews, cotton-grasses, white beak-rush, and bog goldenrod. Forested bogs may have black spruce, balsam fir, and larch as dominants. Associated species include sheep laurel, labrador tea, rhodora, and creeping snowberry. Edges of bogs where minerals are more abundant and water forms a type of moat are called "laggs." They are colonozed by speckled alder and the trees listed above plus northern white cedar, northern wild rasin, blue flag, wild calla, and cinnamon fern.