Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subspeciosiforme F.A.C. Kouwets 2025

This puzzling small taxon was thought by Frans Kouwets (person communication) to be a small form of Cosmarium speciosum var. simplex Nordstedt 1872. Since then, Kouwets (2025) has described this new species which, in my opinion, fits well, if not perfectly, with the taxon under discussion.
Single cell dimensions: L: 35.1 µm; B: 24.4 µm; Is: 13.9 µm; Th: 16.1 µm; L/B: 1.44.
Being newly described, the status in the Outer Hebrides is unknown. The only sample to date has come from moss on wet rocks, which is acidic and oligotrophic.

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