Phycology (or algology), a part of botany, is the study of algae. Algae are important as plants 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 algae); many others are have many cells, some of these being very big, like seaweeds such as kelp and Sargassum.
A phycologist is a person who studies phycology.