Seagrass and Land Plants

Although seagrasses live in marine waters, they evolved millions of years ago from land plants and have many of the same morphological features, such as leaves, roots, flowers, seeds, and conducting tissues. Similar to terrestrial vegetation, seagrasses use the process of photosynthesis to manufacture their own food and produce oxygen through structures called chloroplasts. Land plants have chloroplasts in both the stems and leaves, but in seagrasses, chloroplasts are found only in the leaves. Since seagrasses don't need to overcome the force of gravity, they don't have the strong supportive stems and trunks found in land plants; instead, they depend on the natural buoyancy of the water to provide support. This allows seagrass blades to remain flexible to bend and move with the force of currents and waves. To protect leaves from this high-energy environment, however, seagrasses have developed tube-like structures, called sheaths, which extend down through the vertical rhizome. This structure, not found in land plants, protects the meristem and any newly formed leaves, which extend up through the sheath of previously formed leaves.

Image source: Hemminga, M.A. and C.M. Duarte, 2000. Seagrass Ecology. Cambridge University Press, Cambridge, UK. Modified with permission.