Phylum: Charophyta   Family: Desmidiaceae

Cosmarium hornavanense  Gutwinski 1909

A large desmid with coarse granules along the periphery in face view. The central area is almost lacking in granules but is scrobiculate. The smaller var. janoviense has not been knowingly recorded in the Outer Hebrides as of 2025.
Cell dimensions: L: 81-98 µm; B: 64-72 µm.; Is: 22-28 µm; L/B: 1.19-1.37.
Infrequently recorded in the Outer Hebrides with most records coming from atmophytic habitats, but also from moorland pools.

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