Brown Algae
Brown Algae, about 1500 species of almost exclusively marine, brown-colored algae, known as seaweeds, that make up the brown algae phylum in the protist kingdom. They are found mainly in the tidal zones of temperate to polar seas, but some exist in the deep ocean. Brown algae are the largest of the algae; well-known forms include the giant kelp and the free-floating sargassum weed. Their brown color is derived from the presence of the pigment fucoxanthin, which along with other xanthophyll pigments, masks the green color of the chlorophyll in the algal cells. The brown algae are multicellular and have differentiated structures that, in some species, bear a superficial resemblance to the roots, stalks, and leaves of true plants. These structures, however, are quite different internally. The cell walls of the algae are made of a cellulose similar to that found in red algae; the outsides of the walls are covered by a gelatinous pectic compound called algin. The plants undergo an alterna...