Phylum: Charophyta   Family: Desmidiaceae

Cosmarium ovale J. Ralfs 1848

A distinct and large cell that cannot be confused with any other. The semicells are ovate with a broad base with the sides in face-view furnished with about 20 medium-sized conical granules. Unusually, the chloroplast is parietal.
Cell dimensions (3): L: 180-196 µm; B: 108-111 µm; Is: 38-44; L/B: 1.63-1.82.
A widespread but rarely recorded species. Recent finds in the Outer Hebrides are from slightly acidic, mesotrophic waters. These include vegetated loch-margins, and shallow, silty, lochs.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.
West, W. & West, G.S. (1908). A Monograph of the British Desmidiaceae, Volume 3.