a coarse, olive-brown, branching seaweed, Sargassum bacciferum, common in the Gulf Stream and tropical American seas, characterized by numerous berrylike air vessels.
gulf·weed also gulf weed (gŭlf'wēd') n. Any of several brownish seaweeds of the genus Sargassum of tropical Atlantic waters, having rounded air bladders and often forming dense, floating masses. Also called sargasso, sargassum.