Phylum: Charophyta   Family: Closteriaceae

Closterium pritchardianum W. Archer 1862

First described and illustrated by Archer (1862: 250, pl. 12: 25-27). This is similar to C. acerosum and Coesel & Meesters (2023: 57) suggest this difference is questionable. Interestingly, they give similar habitat requirements for both species, i.e. slightly acidic to slightly alkaline. Whereas Brook & Williamson (2010: 269) differentiate between the two suggesting C. pritchardianum enjoys a more acidic environment. C. pritchardianum also has a larger L/B ratio, but again, there is some overlap with C. acerosum.
Cell dimensions: L: 400-850 µm, B: 30-45 µm, Ap: 5-9 µm; L/B: 10-22.
Proving to be very scarce in the Outer Hebrides.

References: 
Archer, W. (1862). Description of a new species of Cosmarium (Corda), of Staurastrum (Meyen), of two new species of Closterium (Nitzch), and of Spirotaenia (Breb.).
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.