Phycology (from Greek φύκος, phykos, "seaweed"; and -λογία, -logia) or algology (from Latin alga, also "seaweed"), 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). Phycology/algology is the branch of life science that involves the study of algae.
Phycology also includes the study of prokaryotic forms known as blue-green algae or cyanobacteria. A number of microscopic algae also occur as symbionts in lichens.
A phycologist is a person who studies algae as described above. In a similar manner, a mycologist is a person who has been professionally trained in mycology, the study of fungi.