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. They do not flower. 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).
Phycologists typically focus on either freshwater or ocean algae, and further within those areas, either diatoms or soft algae.
While both the ancient Greeks and Romans knew of algae, and the ancient Chinese even cultivated certain varieties as food, the scientific study of algae began in the late 18th century with the description and naming of Fucus maximus (now Ecklonia maxima) in 1757 by Pehr Osbeck. This was followed by the descriptive work of scholars such as Dawson Turner and Carl Adolph Agardh, but it was not until later in the 19th century that efforts were made by J.V. Lamouroux and William Henry Harvey to create significant groupings within the algae. Harvey has been called "the father of modern phycology" in part for his division of the algae into four major divisions based upon their pigmentation.
It was in the late 19th and early 20th century, that phycology became a recognized field of its own. Men such as Friedrich Traugott Kützing continued the descriptive work. In Japan, beginning in 1889, Kintarô Okamura not only provided detailed descriptions of Japanese coastal algae, he also provided comprehensive analysis of their distribution. Although R. K. Greville published his Algae Britannicae as early as 1830, it was not until 1902 with the publication of A Catalogue of the British Marine Algae by Edward Arthur Lionel Batters that the systematic correlation of records, extensive distribution mapping and the development of identification keys began in earnest.