Home / Cyanobacteria / Filaments / Pseudo-branches / Plectonema

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Name derivation:

From the Greek plektos, twisted, plaited, and nema, thread

 

Classification:

Plectonema  Thuret ex Gomont  1892;  15 of 84 species descriptions are currently accepted taxonomically (Guiry and Guiry 2013).

Order Oscillatoriales;  Family Oscillatoriaceae

 

Morphology:

Trichomes of discoid (wider and short) cells with rounded apical cells inside visible sheaths. The filaments often occur coiled in tangled masses. Do not form any specialized cells, but reproduces by hormogonia, sections of the trichome that separate via necridia (dead cells). False branching may be present.

 

Similar genera:

May exhibit double false branching similar to those encountered in Scytonema, which also forms hormogonia; however Scytonema produces heterocysts and Plectonema does not. Cells of Scytonema are cylindrical and isometric in comparison to Plectonema's discoid cells.

Whitton (2011) provides an exhaustive discussion about whether to retain original classic taxonomy of Geitler (1932), which he does, or to accept more recent revisions of filamentous cyanobacteria lacking heterocysts and akinetes (Oscillatoriales) by Komarek and Anagnostidis (2005).  Whitton also describes ecology and morphological variability of this group of genera as affected by their environment, such as phosphate depletion or excess, and light intensity.

Following Geitler, Plectonema is separated from Lyngbya because it has false branching arising from intercalary growth within it rigid sheath.  Lyngbya is separated from Oscillatoria only because it has a visible sheath.  Phormidium is separated from the above by forming dense mats of filaments with aggregate sheaths, and either benthic or planktonic.  Gas vesicles are formed in most planktonic strains but for obvious reasons don’t develop in benthic strains.

 

Habitat:

Among littoral zone plants of oligotrophic lakes and oxygen-rich ponds. One species from North American lakes has been found to contain toxins.

 

References:

Guiry, M.D. and G.M. Guiry  2013.  AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.  http://www.algaebase.org; searched on 28 February 2013.

 

 

 

 

 

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