Phylum: Charophyta   Family: Desmidiaceas

Cosmarium pseudomelanosporum F.A.C. Kouwets 2025

A very small desmid that is quite variable. The apex is about truncate but can be slightly rounded or retuse. The sinus is open and linear to opening widely from the start.
Cell dimensions (3): L: 10.7-11.8 µm; B: 10-11.7 µm; Is: 5.7-5.9 µm; Th: c.5.5 µm; L/B: 1.01-1.09.
Found in slightly acidic to mildly alkaline waters. Distribution in the Outer Hebrides unknown due to earlier confusion with similar species.

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