Any of the brown algae that make up the genus Sargassum.
They are adapted for a free-floating tropical environment, even though many species grow attached to rocks along the coast. The Sargasso Sea , a free-floating mass of seaweed (mostly S. natans ), occurs in the Atlantic Ocean. Sargassums are also known as sea holly because of their highly branched stems with hollow, berrylike floats and many leaflike, sawtooth-edged blades. They are used as fertilizer in New Zealand and as a component of soups and soy sauce in Japan.