Brown algae (Phaeophyta) are multicellular marine seaweeds. They contain photosynthetic pigments, including chlorophyll a, chlorophyll c, $\beta$-carotene, and fucoxanthin, and store energy as laminarin. Structurally, they attach to substrates using holdfasts and possess leaf-like blades and stalks, though these do not represent true plant leaves, stems, or roots.