Phylum: Charophyta   Family: Desmidiaceae

Cosmarium cataractarum (M. Raciborski) B. Eichler 1895

First described by Raciborski (1889: 79, pl. 5) as Cosmarium variolatum var. cataractarum. Eichler (1895: 60) decided it didn’t belong with C. variolatum and raised it to species level. Štastný, J. & Kouwets, F.A.C. (2012: p. 298, figs. 31-37) conducted research using light microscopes and a scanning electron microscope to show clear distinctions between the species.
Cell dimensions: L: 33-45 µm; B: 25-29 µm; Is: 7-10 µm; Th: 17-20 µm; L/B: 1.30-1.55.
It seems to prefer neutral to alkaline, meso-eutrophic habitats but, so far, rarely encountered in the Outer Hebrides.

References: 
Raciborski, M. (1889) Nowe Desmidyje.
Eichler, B. (1895) Materya y do flory wodorostów okolic Miedzyrzeca.
Štastný, J. & Kouwets, F.A.C. (2012) New and remarkable desmids from Europe, taxonomical notes based on LM and SEM observations.
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium.