Sargassum is a genus of brown (class Phaeophyceae) macroalga (seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral reefs. However, the genus may be best known for its planktonic (free-floating) species. While most species within the class Phaeophyceae are predominantly cold water organisms that benefit from nutrients upwelling, genus Sargassum appears to be an exception to this general rule. Any number of the normally benthic species may take on a planktonic, often pelagic existence after being removed from reefs during rough weather. However, two species (S. natans and S. fluitans) have become holopelagic — reproducing vegetatively and never attaching to the seafloor during their lifecycle. The Atlantic Ocean's Sargasso Sea was named after the algae, as it hosts a large amount of Sargassum.