Coastal freshwater marshes are sometimes found in association with salt marshes, especially along the northern coast where there are more rivers, and ponds are fairly numerous. Freshwater marsh plants have adapted to their aquatic environment in several ways. Most species have developed air tubes to their roots, buoyant leaves, or porous leaf coverings that enhance gas exchange. In contrast to salt marshes, freshwater marshes have little if any water movement.
Typical freshwater marsh plants include numerous species of sedges; these grass-like plants often exceed five feet in height. Slough sedge, Carex obnupta, is one of the most common. Familiar cigar-shaped cattails, Typha latifolia, form thick stands and are so proliferous that a single plant can rapidly fill a small pond. Bushy, needle-leaved rushes, Juncus phaeocephalus, are also common. Aquatically adapted wildflowers such as yellow pond-lily, Nuphar polysepalum, with broad oval leaves up to 16 inches in diameter; water buttercup, Ranunculus orthorhynchus; and succulent water parsley, Oenanthe sarmentosa, are also typical freshwater marsh inhabitants.