Anabaena is a filamentous blue-green algae. The filaments (trichomes) are composed of beadlike or barrel-shaped cells that contain akinetes, reproductive cells which have a thick cell wall and a dense concentration of food material. Anabaena are nitrogen fixers - they extract atmospheric nitrogen (N) and incorporate (fix) useful nitrogenous compounds. Sometimes Anabaena can produce deadly toxins.
Anabaena can be differentiated from Nostoc in that they have no definite tegument or membrane enclosing the cell mass, and hence the colony is soft and formless.