Red algae and filamentous green algae are important components of Australian freshwater habitats, such as rivers, streams, lakes, ponds, swamps, farm dams and damp soil. Some are significant primary producers, although occasionally producing weedy problem growths, while others are important sources of food and shelter for large and small fish, turtles, molluscs, crustaceans and insect larvae. Many have restricted distributions, and some an ancient Gondwanic origin. This volume documents three orders of one family, 14 genera and 210 species and infraspecific taxa of red and green freshwater algae. It covers the vast majority of macroscopic freshwater algae likely to be encountered in Australia. The red algal genus Batrachospermum is widespread in pristine streams, as well as in some lakes and swamps, while the filamentous green genera Oedogonium, Bulbothrix, Spirogyra and Zygnema are common and diverse across a broad range of aquatic habitats.