Algae are a large, informal and polyphyletic group of photosynthetic organisms that range from microscopic single cells to giant seaweeds, living chiefly in aquatic and moist environments and lacking the true roots, stems, leaves and vascular tissues of land plants. Once classified together as simple plants, algae are now understood to be scattered across multiple major lineages of life, including bacteria (the cyanobacteria) and several distinct branches of eukaryotes. Despite this lack of common ancestry, they are united by their reliance on photosynthesis—converting light energy into chemic...