Phylum: Charophyta   Family: Desmidiaceae

Cosmarium granatum Ralfs 1848

This taxon and its varieties are quite variably both in shape and size. This nominate variety is generally regarded as the largest in the complex. See the other varieties for more comments.
Cell dimensions: L: 29-45 µm; B: 21-36 µm; Is: 8-10 µm; Th: c.17 µm; L/B: 1.3-1.5.
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: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.
Van Westen, M.C. (2024). Sieralgen in Drenthe.