from Maine Wetlands and Their Boundaries: A Guide For Code Enforcement Officers, by Ralph W. Tiner
Coastal marshes are "grasslands" periodically flooded by tides, primarily salt or brackish tidal water. These marshes are flooded by the tides at various intervals, ranging from once daily to a few times a year. When not flooded, however, the soils remain saturated near the surface at least during the high tide stage. The salinity due to ocean-derived salts creates a salt-stressed aquatic environment that prevents the establishment of most wetland plants. Plants adapted for life in salt water are called "halophytes." Most halophytes actually grow best in fresh water, but are outcompeted by other plants there and forced to live in salt and brackish environments. In more saline areas, coastal marshes called salt marsh are represented by grasses and grasslike plant: smooth cordgrass, salt hay cordgrass, salt grass, salt marsh bulrush, glasswort, black grass, baltic rush, salt marsh sedge, and seaside arrow-grass. Further landward or upstream, brackish marshes dominated by narrow-leaved cattail are found. Seaside goldenrod, prairie cordgrass, and common reed also occur in these situations and along the upper borders of salt marshes. The most upstream coastal marshes are freshwater tidal marshes. They are strictly freshwater wetlands whose water levels fluctuate due to tidal action. Wild rice, cattails, and other freshwater species dominate these tidal marshes, such as those found in Merrymeeting Bay.