Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subcucumoides F.A.C. Kouwets 2025

This recently described species, along with C. subcucumiforme Kouwets 2025, are based on the poorly described C. subcucumis Schmidle 1893. The latter is the larger of the two, but dimensions do overlap a little. More significantly, the latter species has two large pyrenoids per semicell whereas C. subcucumoides has several smaller ones, although not always easy to see.
Single cell dimensions: L: 61.3 µm, B: 42.2 µm, Is: 17 µm; Th: c.24 µm, L/B: 1.46.
Due to taxonomic confusion, the status in the Outer Hebrides is unknown. It would seem to favour mesotrophic, slightly acidic environments.

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