Phylum: Charophyta   Family: Desmidiaceae

Cosmarium trachypleuroides M.C. van Westen & P.F.M. Coesel ex F.A.C. Kouwets 2025

Cells about as long as broad with a sinus closed for the greater part and with a slightly dilated apex. Semicells in frontal view almost oblong with broadly rounded angles. The cell-wall along and within the margin ornamented with small, conical granules. A central protuberance comprises a broken ring of granules biased towards the isthmus with what appears to be just a single granule towards the apex, in the centre is a larger granule. Chloroplast axile with a central pyrenoid.
Single cell dimensions: L: 34.1 µm; B: 33.7 µm; Is: 13.2 µm; Th: c.20 µm; L/B: 1.02.
From Europe the recorded environment is of mesotrophic, slightly acidic waters. The only find from the Outer Hebrides to date (2025) is from a squeeze of floating Potamogeton natans in a shallow pool with a pH of 6.1.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.
Van Westen, M.C. (2024). Sieralgen in Drenthe.