Coastal wetlands support a surprisingly diverse range of plant life, from towering mangrove trees to underwater meadows of seagrass. The exact species depend on the type of wetland, but the major categories include salt marsh grasses and succulents, mangrove trees, seagrasses, and brackish-water species like cattails and bulrushes that thrive where fresh and salt water mix. Each group has evolved remarkable strategies for surviving in salty, waterlogged soil where most land plants would quickly die.
Salt Marsh Grasses, Rushes, and Succulents
Salt marshes are dominated by grasses, sedges, rushes, and fleshy succulent plants. The most iconic group is cordgrass, which forms dense stands along the Atlantic and Gulf coasts of North America. Smooth cordgrass colonizes the lowest elevations of the marsh, where it gets flooded by tides twice a day. Salt meadow cordgrass and sand cordgrass occupy slightly higher ground. These grasses can tolerate regular saltwater flooding that would kill typical lawn or prairie species.
Black rush is another common salt marsh plant, forming thick stands in the upper marsh where flooding is less frequent. Research on southeastern U.S. marshes found that the boundary between cordgrass and black rush comes down to just a few centimeters of elevation. Cordgrass dominates the lower, saltier zone because black rush simply can’t handle that level of flooding. Black rush dominates the upper zone not because cordgrass can’t grow there, but because black rush crowds it out when conditions are less stressful.
Succulent plants like glasswort (sometimes called pickleweed or samphire) are also common in salt marshes. These fleshy plants store water in their thick stems and leaves, which dilutes the salt they absorb and keeps their cells functioning. Some succulent species actually become fleshier as soil salinity increases, up to a point. Glasswort species are found in salt marshes worldwide and are even eaten as a sea vegetable in some coastal cuisines.
How Salt Marsh Plants Survive High Salinity
Plants that live in salty environments are called halophytes, and they use several distinct strategies to cope with salt. Some, like cordgrass, have tiny salt glands on their leaves that actively pump excess salt out of the plant. If you look closely at cordgrass blades on a dry day, you can sometimes see salt crystals on the surface. Other halophytes block salt at the root level, preventing it from traveling up into leaves and stems where it would interfere with photosynthesis.
A third strategy is compartmentalization. These plants absorb salt but lock it away inside specialized cellular compartments, keeping it separated from the machinery that keeps the cell alive. Many halophytes combine multiple strategies. Their leaves also tend to be thick, waxy, or hairy, all features that reduce water loss in an environment where, despite being surrounded by water, absorbing fresh water is difficult because of the high salt concentration in the soil.
Mangrove Trees
Mangroves are the only trees that grow directly in saltwater. Three species dominate in North America: red mangrove, black mangrove, and white mangrove. Each occupies a slightly different position along the shoreline.
Red mangroves grow closest to the water and are easy to recognize by their arching prop roots, which extend three feet or more above the soil surface. These roots stabilize the tree in soft mud and deliver oxygen to the underground root system. Red mangroves can reach over 80 feet tall in ideal conditions, though in Florida they typically average around 20 feet. Their seeds are unusual: they sprout while still attached to the parent tree, growing into pencil-shaped seedlings about six inches long before dropping into the water to float and colonize new areas.
Black mangroves grow at slightly higher elevations, where the roots are exposed to air between tides. Their most distinctive feature is pneumatophores, pencil-shaped projections that stick up from the mud around the base of the tree like snorkels. These structures pull oxygen from the air and channel it down to the waterlogged roots below. Black mangroves can reach 50 feet in Florida and are more cold-tolerant than red mangroves, extending farther north along both coasts.
White mangroves occupy the highest ground of the three and lack the dramatic aerial root systems of their relatives. They’re the least cold-tolerant species, restricted to southern Florida. Their broad, flat leaves have small sugar-secreting glands at the base, and they produce greenish-white flower spikes in spring and early summer. When flooded for long periods, white mangroves can develop short peg roots to access oxygen, but in drier conditions they look more like an ordinary shrub or small tree.
Seagrass Meadows
Seagrasses are flowering plants that live entirely underwater, rooted in sandy or muddy seafloor in shallow coastal waters. They’re not seaweed (which are algae) but true plants with roots, leaves, and flowers. Along the Gulf Coast, three species dominate: turtle grass, manatee grass, and shoal grass.
Turtle grass is the largest and most robust of the three, with wide, ribbon-like blades. It forms dense meadows in subtidal areas where it’s never exposed to air. Manatee grass has thin, cylindrical leaves and often grows mixed in with turtle grass. Shoal grass has narrow leaves and is considered the pioneer species of seagrass beds. It’s the first to colonize bare sediment and can tolerate shallower water where its leaves get exposed to air at low tide. It also handles lower salinity better than the other two, so it tends to grow in areas closer to freshwater sources.
Along the Atlantic Coast and into cooler northern waters, eelgrass is the dominant seagrass species. It forms extensive underwater meadows from North Carolina up through New England and along the Pacific Northwest coast. These meadows provide critical habitat for fish, shellfish, and sea turtles.
Brackish Water Transition Plants
Where rivers meet the coast, salinity drops and a different set of plants takes over. These brackish zones, often called tidal freshwater marshes, support species that can handle some salt but not full-strength seawater. Broadleaf cattail is one of the most recognizable, growing in brackish marshes from the San Francisco Bay to southern Florida and the Carolina coast. It tolerates salt levels up to about 1%, well below full ocean salinity (around 3.5%) but far higher than most freshwater plants can manage.
Bulrushes, particularly hardstem bulrush, also thrive in these transitional zones. In the San Francisco Bay area, bulrush-cattail marshes are a common plant community. Along the North Carolina Coastal Plain, cattails mix with black rush in tidal freshwater communities, creating a visible gradient from salt-tolerant species near the ocean to freshwater species farther upstream.
Common Reed: A Widespread Invader
Not all plants in coastal wetlands belong there. Common reed is a tall wetland grass found on every continent, and while a native lineage exists in North America, an invasive lineage introduced from Eurasia has been aggressively expanding into both coastal and inland wetlands. It outcompetes native vegetation, forming dense single-species stands that reduce plant and animal diversity. Around Utah’s Great Salt Lake, common reed now occupies more than 36 square miles of wetland after floods in the 1980s gave it a foothold.
The plant thrives especially well in nutrient-rich conditions, growing more vigorously and producing more seed heads where nitrogen levels are high. It spreads through underground stems and runners, making it extremely difficult to remove once established. Land managers across North America consider it one of the most problematic invasive species in wetland habitats.
Why These Plants Matter for the Climate
Coastal wetland plants do more than hold shorelines together. Salt marshes store an average of about 8.0 metric tons of CO₂ per hectare per year, and mangroves store roughly 8.3 metric tons. These rates are remarkably high compared to most terrestrial ecosystems, which is why coastal wetland vegetation is often called “blue carbon.” The plants pull carbon dioxide from the atmosphere through photosynthesis, and much of that carbon ends up buried in waterlogged soil where it decomposes extremely slowly, locking it away for centuries or longer. Losing these habitats doesn’t just eliminate the plants and wildlife. It releases stored carbon back into the atmosphere, turning a carbon sink into a carbon source.