Phylum: Charophyta   Family: Desmidiaceae

Cosmarium speciosum var. simplex C.F.O. Nordstedt 1872

C. speciosum is a species complex with a broad size-range. Variety simplex was named for the simple granules (as opposed to var. biforme with emarginate granules). However, intermediate forms have been found confusing the situation. More finds are needed to evaluate the taxa involved.
Single cell dimensions: L: 45.4 µm; B: 28 µm; Is: 16.7 µm; L/B: 1.63.
Because of the confusion mentioned above, the status in the Outer Hebrides is unknown. The only sample to date has come from an acidic shallow boggy pool.

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