Around 100 million years ago, grass from land adapted to live and reproduce while submerged in seawater—the modern-day seagrasses. This sea invasion by land plants happened four separate times, resulting in four unrelated families of 50-60 total seagrass species, which can be found on the coast of every continent except Antarctica. Just like grasses on land, seagrasses form vast meadows, produce flowers and seeds, and are home to an incredibly diverse community of organisms.
Seagrasses are found around the world, in tropical and colder regions. Shades of green indicate numbers of species reported for an area. (from 2005 UNEP-WCMC).