Phylum: Charophyta   Family: Desmidiaceae

Cosmarium arvidsjaurense F.A.C. Kouwets 2025

A very large cell with broadly sub-pyramidate semicells. Sinus closed for the first part with a dilate apex, then opening widely. Lower half of sides broadly rounded then converging to a slightly raised apex. Cell-wall thick and granulate with about 22-24 granules visible in face-view per semicell. Granules are relatively small and sparse on the facial surfaces.
Single cell dimensions: L: 110 µm; B: 82 µm; Is: 30 µm; Th: c.50 µm; L/B: 1.35.
An Arctic-alpine species of rare occurrence. It favours slightly acidic mossy moorland pools and bogs.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.