Phylum: Charophyta   Family: Desmidiaceae

Cosmarium discrepans J. Stastny & F.A.C. Kouwets 2012

This size and shape of the semicell is characteristic of several species and a close look at the granular structure and disposition is required. It mostly resembles C. subpunctulatum Nordstedt 1887 both in morphology and size but with a coarser granulation.
Cell dimensions: L: 30.5-35 µm; B: 25.6-31.8 µm; Is: 9.6-12 µm; Th: c.17-19 µm; L/B: 1.13-1.21.
Probably not scarce but likely to have been misidentified in the past. It prefers acidic habitats such as moorland pools and bogs plus abandoned peat-cuttings.

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