Phaeophyta, commonly known as brown algae, are a group of marine organisms primarily found in cold coastal waters. They are characterized by their brown color, which comes from the pigment fucoxanthin. Brown algae can vary in size from small filaments to large seaweeds, such as kelp, which can grow up to 60 meters long. These organisms play a crucial role in marine ecosystems, providing habitat and food for various marine species. Phaeophyta also contribute to the global carbon cycle and are used in various industries, including food and cosmetics, due to their nutritional and thickening properties.