Algae is the informal name given to a large group of eukaryotic organisms that use photosynthesis to produce energy. Different species of algae may actually only be distantly related, but they tend to share similar characteristics. Included in this group are organisms ranging from single-celled microalgae and diatoms all the way to the enormous giant kelp, that can grow to 45 m or more. Algae can grow in both freshwater and saltwater and are different from land plants because they don't have roots, stems, and leaves.
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