Phylum: Charophyta   Family: Desmidiaceae

Cosmarium perdepressum F.A.C. Kouwets 2025

A recently described small cell characterised by depressed semicells. Very similar to C. lamouraense, the main difference is in the shape of the basal angle, slightly more rounded in C. perdepressum giving a more open sinus at the exit point.
Cell dimensions (2): L: 18.6-20.9 µm; B: 20.4-21.3 µm; Is: 5.-5.9 µm; Th: 9.5-10.8 µm; L/B: 0.93-0.99.
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.