ANABAENA

genus of nitrogen-fixing blue-green algae with beadlike or barrellike cells and occasionally an enlarged cell (heterocyst), found as plankton in shallow water and on moist soil. There are both solitary and colonial forms, the latter resembling a closely related genus, Nostoc. In northern latitudes during the summer months Anabaena may form water blooms that remain suspended instead of forming a surface scum. A toxic substance produced by Anabaena is fatal to cattle and other animals if present in drinking water in sufficient concentration.