Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subtumidiforme F.A.C. Kouwets 2025

A small desmid with sinuses closed for the most part with dilate apices, semicells depressed reniform with broadly rounded sides, apex truncate to slightly rounded, occasionally retuse. Chloroplast axile with one pyrenoid. Zygospore globose with stubby, pyramidate projections with rounded to slightly capitate apices.
Cell dimensions: L: 19.8-21.5 µm, B: 18.4-19.5 µm, Is: 6.2-7.3 µm; Th: 10.8 µm, L/B: 1.08-1.12.
Zygospore diameter: 24.6-27.6 µm; projections: 4.3-5.5 µm; overall: 34.5-36.7 µm.
Found in mesotrophic, slightly acidic, waters such as moorland pools and loch-margins. Its status in the Outer Hebrides is vague due to possible misidentifications in the past.

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