Phylum: Charophyta   Family: Desmidiaceae

Cosmarium laeve L. Rabenhorst 1868

Rabenhorst's original description (1868: 161 – lacking a drawing) is rather brief and sketchy, which has led to confused interpretations and spawned many varieties, creating a rather confused complex. The taxon depicted below seems to match Kouwets’ (in manuscript) description of his proposed C. laeviforme.
Cell dimensions: L: 27-34 µm; B: 19-23.5 µm; Is: 5.5-8 µm; Th: 12-15 µm; L/B: 1.4-1.5.
Found in circumneutral to more acidic habitats.

References: 
Kouwets, F.A.C. (in manuscript). European Flora of the Desmid Genus Cosmarium.
Rabenhorst, L. (1868). Flora europaea algarum aquae dulcis et submarinae. Sectio III. Algae chlorophyllophyceas, melanophyceas et rhodophyceas complectens.