Phycology (or algology) (from Greek: φύκος, phykos, "seawee"; and λόγος, logos, "knowledge"), a subdiscipline of botany, is the scientific 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 distinguished from the higher plants by a lack of true roots, stems or leaves. Many species are single-celled and microscopic (including phytoplankton and other microalgae); many others are multicellular to one degree or another, some of these growing to large size (for example, seaweeds such as kelp and Sargassum).