Anabaena variabilis is a species of filamentous cyanobacterium. This species of the genus Anabaena and the domain Eubacteria is capable of photosynthesis. This species is heterotrophic, meaning that it may grow without light in the presence of fructose. It also can convert atmospheric dinitrogen to ammonia via nitrogen fixation. Anabaena variabilis is also a model organism for studying the beginnings of multicellular life due to its filamentous characterization and cellular-differentiation capabilities.