褐藻, or brown algae, are a group of marine plants that belong to the phylum Ochrophyta. They are typically found in cold, coastal waters and can vary in size from small filaments to large seaweeds like kelp. Brown algae are characterized by their brownish color, which comes from the pigment fucoxanthin, and they play a crucial role in marine ecosystems as primary producers. These organisms provide habitat and food for various marine species, including fish and invertebrates. Additionally, brown algae are harvested for their economic value, being used in products like agar, carrageenan, and as a food source in many cultures. Their ecological importance and versatility make them significant in both natural and human contexts.