Phylum: Charophyta   Family: Desmidiacea

Cosmarium elevatum (C.F.O. Nordstedt) R. Gutwinski 1895

This species supports a central protuberance, rather like a papilla, per semicell. Compare with the similar-shaped C. elevatiforme Kouwets 2025 but that species is smaller without overlap.
Cell dimensions (2): L: 31.7-32.8 µm; B: 30.6-31.2 µm; Is: 10.6 µm; Th: 18.9 µm; L/B: 1.04-06.
The only samples to date have come from slightly acidic waters. The status is unknown due to earlier taxonomic confusion, but it has been suggested that it’s rare with an Arctic-alpine distribution.

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