Phylum: Charophyta   Family: Desmidiaceae

Cosmarium pseudopyramidatum P.M. Lundell 1871

This species has been at the core of a confused complex, but Kouwets (2025) has broken it down into readily identifiable separate taxa. The main feature of this species is one large pyrenoid per semicell.
Cell dimensions: L: 42-56 µm; B: 28-36 µm; Is: 10-14 µm; Th: c.22; L/B: 1.5-1.6.
In the Outer Hebrides, it is infrequently recorded. Found in moorland pools and bogs.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.