Seaweeds look like plants. They even make their own food from sunlight, like plants do. But seaweeds are not plants. They do not have true roots, stems, leaves, or flowers. They are special types of living things called algae.
Seaweeds are built well for a life in the sea. They are soft and flexible and can sway in the water without being torn apart. Some seaweeds use a root-like anchor to cling to rocks, shells, or the sea floor. Some have gas-filled swellings to keep afloat. Sargassum weed floats in large masses in the ocean. Eel grass grows in thick beds at the muddy bottom of shallow waters. It looks like a field of waving grass along the shore. There are also underwater forests of kelp that grow up from the shallow sea floor.
Some kinds of algae are so small that you need a microscope to see them. And some of them can move around. They do this by beating little hairs that grow from their surface. Sometimes these tiny algae cling together in chains or gather into jellylike balls.
Picture Credit : Google