Phylum: Charophyta   Family: Desmidiaceae

Cosmarium mitriforme F.A.C. Kouwets 2025

A recently described species derived from the C. granatum complex, named after a bishop’s ceremonial headwear.
Cell dimensions: L: 29.4-34.3 µm; B: 20.3-23 µm; Is: 6.0-8.4 µm; Th: 14.7-16.7 µm; L/B: 1.37-1.5.
Because of earlier confusion with similar species, the status and distribution in the Outer Hebrides is unknown. Kouwets (2025: 343) gives acidic, oligo-mesotrophic environments as the preferred habitat, but current finds from the Outer Hebrides have come from semi-permanent rainwater pools in a disused quarry, which is very slightly alkaline. Also found in shallow mesotrophic waters.

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