Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subundulatum J.N.F. Wille 1881

A large desmid with sinuses closed for the most part with slightly dilate apices. Semicells about semicircular with 10 undulations in face view including the apex, the apex has a central dent. Chloroplast axile with two pyrenoid.
Cell dimensions: L: 55-59.5 µm; B: 41-43.4 µm; Is: 18-19 µm; Th: c.30 µm; L/B: 1.34-1.40.
Acidophilic from moorland pools and loch margins, also from abandoned peat-cuttings. Infrequently recorded for the Outer Hebrides.

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