Phaeophyta, commonly known as brown algae, is a division of primarily marine algae characterized by their brown pigmentation due to the presence of fucoxanthin. They are primarily found in cold coastal waters and can range from microscopic phytoplankton to large seaweeds, such as kelp. Brown algae play a significant ecological role, providing habitat and food for marine organisms, and are also utilized in various industries for their alginates and other compounds.