Phylum Phaeophyta

This phylum contains the brown algae, Sargassum, and the various species of kelp. Brown algae are the largest protists, and are nearly all marine. Kelp blades can stretch up to 100 meters long. Brown algae have thin blades with a central midrib or stipe. Like all algae, their blades are thin because they lack the complex conductive tissues of green plants (phloem), and must rely on simple diffusion, though some kelp have phloem-like conducting cells in the midrib. Kelp form the basis of entire ecosystems off the coast of California and in other cool waters. In the Sargasso Sea, the Atlantic Ocean northeast of the Caribbean Islands, the brown algae Sargassum forms huge floating mats, said in older days to trap entire ships, holding them tight until the crew met a watery grave.