Phylum: Charophyta   Family: Closteriaceae

Closterium ehrenbergii J. Ralfs 1848

First described in Ralfs (1848: 166, pl. 28: 2) and illustrated by Jenner. The largest British species in the genus and extremely variable: size can be less than 250 to over 1000 µm; apices can be narrowly rounded to broadly rounded; habitat is mixed hence also the pH - either side of neutral. Modern authors regard it as a biological species-complex.
My cell dimensions: L: 617-757 µm; B: 99-109 µm; Ap: 19-27 µm; L/B: 6-7.
The Outer Hebridean specimens were recorded from a peaty ditch, but rarely found.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Ralfs, J. (1848). The British Desmidieae.
West, W. & West, G.S. (1904). A Monograph of the British Desmidiaceae, Volume 1.