Correct! Seaweed is a complex algae. Although much less common, seagrasses are true plants (which evolved from terrestrial plants like 100 million years ago). I

Correct! Seaweed is a complex algae. Although much less common, seagrasses are true plants (which evolved from terrestrial plants like 100 million years ago). I can't think of any other submerged marine plants, and some limited google searches are only giving me mangrove forests as additional marine plants.