Phylum: Charophyta   Family: Desmidiaceae

Cosmarium boreoquadratum F.A.C. Kouwets 2025

This recently described species was part of the Cosmarium quadratum Ralfs 1848 complex. It’s the largest cell in the group and, as the epithet suggests, has probably an Arctic-alpine distribution.
Single cell dimensions: L: 73.6 µm; B: 38 µm; Is: 20 µm; Th: c.30-33 µm; L/B: 1.94.
Because of the foregoing the status is uncertain. From the little data available it would seem to prefer acidic, boggy habitats.

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