Phaeophyceae, commonly known as brown algae, are a group of marine organisms primarily found in colder ocean waters. They are characterized by their brown color, which comes from the pigment fucoxanthin, and can vary in size from small filaments to large seaweeds like kelp. Brown algae play a crucial role in marine ecosystems, providing habitat and food for various marine species. These algae are important for human use as well, being harvested for food, fertilizers, and industrial products. They are rich in nutrients and are often used in dishes like sushi. Additionally, Phaeophyceae contribute to carbon fixation, helping to mitigate climate change by absorbing carbon dioxide from the atmosphere.