algal bloom




Examples of Anabaena

anabaena (image 1)

400X total magnification; 10 μm scale bar.

anabaena (image 2)

400X total magnification; 10 μm scale bar.


Filaments solitary or joined into clusters, amorphous mats, or in the tissues of aquatic plants; usually entangled and irregularly situated, but sometimes roughly parallel. Sheaths are diffuse, colorless mucilaginous envelopes; never firm. Trichomes usually flexuous to irregularly coiled, sometimes more or less straight; isopolar; sometimes narrowing slightly towards the ends; constricted at the crosswalls; uniseriate. Cells spherical, cylindrical, or barrel-shaped; sometimes with granular content; always without aerotopes; pale to bright blue-green to yellow-green.

Trichomes metameric. Heterocytes solitary, intercalary; spherical, oval, or cylindrical in shape; rarely more than 9 per filament. Akinetes develop paraheterocytically, directly adjacent to heterocytes on either side or distant from heterocytes; usually cylindrical or oval, but rarely spherical; intercalary; solitary or in rows of up to 5; epispore smooth or textured, colorless or yellowish-brown.


Mostly benthic; mat-forming in littoral zone, or on sediments or aquatic plants; in freshwater pools, ponds, or saline lakes.

Note that planktic species with aerotopes, though once classified as Anabaena, have been reclassified; many belong to the genus Dolichospermum (some have been further reclassified; the genus Sphaerospermopsis was separated from Dolichospermum).


  • Johansen, J. R., & Komárek, J. (2015). Filamentous Cyanobacteria. In J. D. Wehr, R. G. Sheath, & J. P. Kociolek (Eds.), Freshwater Algae of North America: Ecology and Classification (2nd ed., pp. 183-218). Waltham, MA: Elsevier.
  • Komárek, J. (2013). Cyanoprokaryota-3. Teil/Part 3: Heterocytous Genera (J. R. Johansen, Ed.). In B. Büdel, G. Gärtner, L. Krienitz, & M. Schagerl (Eds.), Süßwasserflora von Mitteleuropa (Vol. 19/3, pp. 790-792). Heidelberg, Germany: Springer Spektrum.