Phylum: Charophyta   Family: Desmidiaceae

Xanthidium variabile (O. Nordstedt) W. & G.S. West 1900

First described by Nordstedt (1887: 159) as Xanthidium smithii var. variabile. It was later raised to species level by West & West (1900: 291).
Cell dimensions: L: 20-26 µm; B: 18-23 µm; Is: 7.5-9.5 µm; Sp: 2-3.4 µm; overall LxB: 24-26.6 x 23-30.
An acidophile mainly from moorland pools and bogs, especially with Sphagnum. It's proving to be rather scarce in the Outer Hebrides even though we have ideal habitat.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Nordstedt, O. (1887). Algologiska småsker ... 4. Utdrag ur ett arbete öfver de af D:r. S. Berggren på Nya Sealand och i Australien samlade sötvattebsakgerna.
West, W. & West, G.S. (1900). Notes on freshwater algae. II.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.