Abstract
Phycology is the study of algae. However, just what algae are is difficult to define, because they belong to many different and diverse taxonomic groups and include both prokaryotic and eukaryotic representatives. Broadly speaking, the algae comprise all, mainly aquatic, plants and plant-like chlorophyll a-containing organisms that can use light energy to fix carbon from atmospheric carbon dioxide (CO2) and evolve oxygen, but which are not specialised land plants like mosses, ferns, coniferous trees and flowering plants. This is a negative definition, but it serves its purpose. Besides being a principal source of oxygen, algae are important primary producers in many, mainly aquatic, habitats. The prokaryotic Cyanobacteria are important as nitrogen fixers, converting N2 to organic nitrogen. The algae are the source of a number of important commercial products and molecules and are also used in wastewater treatment, as animal feed and as fertilisers.