Phaeophyta (Brown algae)
The 1,500 species of brown algae are almost exclusively found in marine habitats. The browns include the largest of the seaweeds, Durvillea and the kelps, found in cold waters. The kelps present the most complex anatomy of all the algae with trumpet hyphae and sievelike cells that contribute to translocation. The brown algae have chlorophyll a and c, as well as carotenes and xanthophylls. Cell walls are composed of cellulose layered with polysaccharide (such as the valuable alginic acid.) Brown algal cells have a single nuclei and thylakoids in the chloroplast occur in bands of three. Most brown algae produce a motile cell (zoospores or gametes, or both).