While they may look similar, seagrasses are very different from seaweeds, which are a type of organism known as algae, not a flowering plant. Seagrasses are part of a group of plants called monocotyledons. This group of plants also includes the grasses that grow on land, lilies (seagrasses' closest relative), and palms. Seagrasses have roots, veins, and leaves. Seagrasses, like other plants, have special food producers inside their cells, called chloroplasts. Chloroplasts use energy from the sun to convert carbon dioxide and water into sugar and oxygen for growth, through the process called photosynthesis. Veins inside the seagrass tissue then transport the sugar and oxygen around the plant. The veins also contain air pockets, called lacunae, that help keep the seagrass leaves floating in the water. Seagrasses have roots and rhizomes (thicker stems), which extend into the sediment below the leaves. The roots and rhizomes absorb and store nutrients and help to anchor the seagrass plants (and sediment) in place. Seaweeds, however, are much less complex than seagrasses, with no flowers or veins.

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