Seagrasses are flowering land plants that returned to the ocean millions of years ago

Gardening · Published 3 October 2026 Swipe more like this →

In short: Seagrasses are not seaweed, but true flowering plants that evolved from terrestrial ancestors to live fully submerged in shallow coastal waters. Found on every continent except Antarctica, these underwater meadows act as vital carbon sinks, stabilize the seafloor, and provide essential nursery habitats for diverse marine life.

Seagrasses are unique marine angiosperms that evolved from terrestrial monocots between 70 and 100 million years ago. Unlike algae, they possess true roots, leaves, flowers, and seeds. To survive in the ocean, they underwent significant physiological changes, such as losing stomata and adapting their cell walls to handle high salinity and anoxic conditions. While they resemble terrestrial grasses, they are specialized plants that thrive in the photic zone of sheltered bays, estuaries, and lagoons.

These meadows are among the most productive ecosystems on Earth. Species like eelgrass, turtle grass, manatee grass, and shoal grass play distinct roles in their environments. Shoal grass, for instance, is a pioneer species that colonizes disturbed sandy areas, helping to stabilize sediment and prepare the seafloor for other vegetation. Turtle grass and manatee grass provide critical food sources for grazers like green sea turtles and manatees, while their dense blades offer cover for juvenile fish, scallops, and invertebrates.

Beyond their role as habitat, seagrasses provide essential ecosystem services, including water filtration and the storage of blue carbon. By slowing water movement, they trap sediment and maintain water clarity, which is vital for their own survival as they require sunlight to photosynthesize. Despite their importance, these meadows face significant threats from coastal development, pollution, and rising ocean temperatures. Current restoration efforts in national marine sanctuaries focus on improving water quality and protecting these delicate underwater pastures from physical damage.

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