Sargassum natans is a species of brown algae in the family Sargassaceae. In English the species goes by the common names common gulfweed, narrowleaf gulfweed, or spiny gulfweed.

It occurs in the Sargasso Sea. It is also pelagic and reproduces by fragmentation. It, along with Sargassum fluitans, have been credited with plaguing beach tourism industry in Yucatán and South Florida.

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