OK, I have to admit that this one was a trick question. This is Sargassum, also known as Sargasso Weed. It is a type of algae, which means that it does not have leaves, even though it has leaf-like structures. It is not even classified as a plant, although it used to be. It is now in phylum Heterokonta, which also includes diatoms.
It does have air bladders that make it float, often in large mats. There are many specialized creatures that live in Sargassum. Quite a few of them have colors and shapes that match the algae. It is also bioluminescent, and gives off a bright green light when you step on it during night walks on the beach.