Mannitol is a complex carbohydrate used as stored food in Phaeophyceae (Brown Algae). Fucus is a brown alga . In contrast, Gracilaria and Porphyra are Rhodophyceae (Red Algae) which store food as Floridean starch , and Chara is a Chlorophyceae (Green Algae) which typically stores food as starch .