algal bloom




Examples of Rivularia

rivularia (image 3)

100X total magnification; 10 μm scale bar.

rivularia (image 4)

100X total magnification; 10 μm scale bar.

rivularia (image 2)

400X total magnification; 10 μm scale bar.

rivularia (image 1)

400X total magnification; 10 μm scale bar.


Colonies attached to substrate; younger colonies hemispherical to nearly spherical, and sometimes hollow; later fusing with other colonies into macroscopic growth composed of flat, irregular, or hemispherical layers; colonial slime usually with a firm margin; thallus gelatinous or encrusted with calcium carbonate; unencrusted colonies sometimes hollow. Filaments are radially and parallely arranged; rather densely arranged; bases of filaments are at first oriented towards the colony center, and are later oriented towards the substrate. Trichomes with mucilaginous, colorless to yellow-brown sheaths, sometimes becoming confluent; filaments usually remaining enclosed by the sheath of the mother trichome; sheaths often widened, opened at the apical ends, often not enclosing the apical end of the filament. Trichomes heteropolar, widened at the base, with basal heterocytes, and narrowed to an apical hair; constricted or unconstricted at crosswalls; false branches arise at intercalary heterocytes, growing roughly in parallel with the mother trichome, but soon separating. Cells cylindrical or barrel-shaped; narrowed and elongated in the apical hairs; without aerotopes.

Obligatory heterocytes; spherical to hemispherical; basal, or occasionally intercalary, especially before false branch formation; solitary, or rarely paired. Akinetes are not present.


Mostly epilithic or epiphytic; particularly on calcerous substrates. Many species inhabit unpolluted, stagnant and flowing freshwater. Several marine species inhabit rocky littoral zones.


  • 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. 183-190). 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. 286-287). Heidelberg, Germany: Springer Spektrum.