Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subtumidum var. groenbladii H.T. Croasdale 1964, sensu Lenzenweger 1987

This variety is generally larger than the nominate with the cell-wall thickened near the lateral angles and is coarsely punctate.
Cell dimensions: L: 31-41 µm; B: 26-34 µm; Is: 10-11.5 µm; Th: 18-22 µm; L/B: 1.18-1.36.
This taxon has rarely been found in the Outer Hebrides but may have suffered from misidentifications. Found in the tychoplankton of slightly acidic, mesotrophic lochs and pools.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.
Lenzenweger, R. (1987). Beitrag zur Kenntnis der Zieralgenflora des Salzburger Lungaues.