Phylum: Charophyta   Family: Desmidiaceae

Cosmarium granatum J. Ralfs 1848

This taxon is part of a complex, which Kouwets (2025: 245) has made good progress in sorting out. He has named new species and renamed some of the varieties. This nominate variety is generally regarded as the largest in the complex.
Cell dimensions: L: 31.2-49.7 µm; B: 21.8-34 µm; Is: 8.3-12.5 µm; Th: c.17 µm; L/B: 1.43-1.47.
Found in mesotrophic, circumneutral waters. Status in the Outer Hebrides unclear due to confusion with similar species, but at present it is infrequently recorded.

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