Phycology (or algology), a part of botany, is the study of algae. Algae are important as primary producers in aquatic ecosystems. Most algae are eukaryotic, photosynthetic organisms that live in a wet environment. They are different from the higher plants by a lack of "normal" roots, stems or leaves. Many types have one cell and are very small or microscopic (including plankton and other microalgae); many others have many cells; some of these are very big, like seaweeds such as kelp and "Sargassum".