Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subgranatum (C.F.O. Nordstedt) J. Lütkemüller 1902

The original concept of the taxon by Nordstedt (1878: 13) as C. granatum var subgranatum is somewhat confused. Lütkemüller (1902: 364) raised it to species level and gave it a clearer definition. This species has pyramidal semicells unlike the variety borgei which has hemispherical semicells. Most cells found in the Outer Hebrides have 10 undulations per semicell but occasionally 8 undulations are encountered. Given the variability in the shape of the semicells, it can be confused with C. impressulum.
Cell dimensions: L. 20-31 µm; B. 14-24 µm; Is. 4.5-8 µm; Th. 13-14 µm; L/B. 1.2-1.6.
Infrequently recorded, found in the plankton of circumneutral waters.

References: 
Kouwets, F.A.C. (in manuscript). European Flora of the Desmid Genus Cosmarium.
Lütkemüller, J. (1902). Die Zellmembran der Desmidaceen.
Nordstedt, C.F.O. (1878). De algis aquæ dulcis et de Characeis ex insulis Sandvicensibus a Sv. Bergren 1875 reportatis.
Van Westen, M. (2024). Sieralgen in Drenthe.