Thalassia testudinum, commonly known as turtlegrass, is a species of marine seagrass in the family Hydrocharitaceae. It forms meadows in shallow, sandy water in locations in the Caribbean Sea and the Gulf of Mexico. Turtle grass and other seagrasses form meadows which are important habitats and feeding grounds. The grass is eaten by turtles and herbivorous fish, supports many epiphytes, and provides habitat for juvenile fish and many invertebrate taxa.