They include many seaweeds, including the familiar wracks and bladder wrack, and the kelps, including the largest of all brown algae, Macrocystis ??? a genus of kelp that grows to more than 100m (320ft) at up to 0.5 (18in) per day.Sargassum forms vast floating masses in the Sargasso Sea in the mid-Atlantic, with their own distinctive communities of animals and microorganisms.