Sargassum occurs. "Sargassum muticum" is a large brown seaweed of the class Phaeophyceae. It grows attached to rocks by a perennial holdfast up to 5 cm in diameter. From this holdfast the main axis grows to a maximum of 5 cm high. The leaf-like laminae and primary lateral branches grow from this stipe. In warm waters, it can grow to 12 m long, however in British waters it gives rise to a single main axis with secondary and tertiary branches that the plant sheds annually. Numerous small 2–6 mm stalked air vesicles provide buoyancy. The reproductive receptacles are also stalked, and
Sargassum and "S. fluitans") have become holopelagic—reproducing vegetatively and never attaching to the seafloor during their lifecycles. The Atlantic Ocean's Sargasso Sea was named after the algae, as it hosts a large amount of "Sargassum". "Sargassum" was named by the Portuguese sailors who found it in the Sargasso Sea after the wooly rock rose ("Halimium lasianthum") that grew in their water wells at home, and that was called "sargaço" in Portuguese (). The Florida Keys and its smaller islands are well known for their high levels of "Sargassum" covering their shores. Gulfweed was observed by Columbus. Although it was formerly thought