Mannitol is a food stored in Fucus. Fucus is a genus of brown alga in the class Phaeophyceae to be found in the intertidal zones of rocky seashores almost everywhere in the world. Primary chemical constituents of this plant include mucilage, algin, mannitol, beta-carotene, zeaxanthin, iodine, bromine, potassium, volatile oils, and many other minerals.