Planktothrix

Taxonomy

Order Oscillatoriales
Family Microcoleaceae
Genus Planktothrix

Morphology

Solitary (or forming clusters or clumps when in dense blooms), free-floating trichomes. Trichomes straight to slightly curved or waved; isopolar; cylindrical; mostly not constricted at crosswalls, but sometimes slightly constricted; usually long, reaching up to 4 mm in length, and (2.3) 3-12 (15) μm wide; without any branching; sometimes slightly attenuated at the ends. Immotile, or sometimes with subtle gliding or trembling. In most species, (fine) sheaths occur only sometimes, in culture or in response to suboptimal environmental conditions; one species (P. cryptovaginata) usually has fine, colorless sheaths. Cells cylindrical or rarely somewhat barrel-shaped; typically a bit shorter than wide or roughly isodiametric, rarely longer than wide; fully developed apical cells widely rounded or narrowed-conical, sometimes with calyptra or with thickened outer wall, sometimes capitate in some species. Aerotopes distributed throughout cells; trichomes sometimes contain segments of cells lacking aerotopes, which appear paler/lighter than the rest of the trichome. 

Ecology

Mostly planktic, rarely metaphytic; in lakes, ponds, reservoirs, stagnant waters. Some species are capable of forming surface blooms.

References

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. 162-168). Waltham, MA: Elsevier.

Komárek, J. & Anagnostidis, K. (2008). Cyanoprokaryota-2. Teil/Part 2: Oscillatoriales. In B. Büdel, G. Gärtner, L. Krienitz, & M. Schagerl (Eds.), Süßwasserflora von Mitteleuropa (Vol. 19/2, pp. 354-361). Heidelberg, Germany: Spektrum.

Strunecký, O., Ivanova, A.P., & Mareš, J. (2023). An updated classification of cyanobacterial orders and families based on phylogenomic and polyphasic analysis. Journal of Phycology, 59: 12-51. https://doi.org/10.1111/jpy.13304