The largest and most complex algae are brown algae. All are multicellular, and most are marine. Brown algae are especially common along temperate coasts, where the water is cool. They own their characteristic brown or olive color to the carotenoids in their plastids. Many species commonly called "seaweeds" are brown algae. (Some large, multicellular species of red and green algae are also referred to as seaweeds.) Brown algae include species that have the most complex multicellular anatomy of all algae; some even have specialized tissues and organs that resemble those in plants.