Phylum: Charophyta   Family: Closteriaciaea

Closterium angustatum var. gracilius H.T. Croasdale 1955

First described and illustrated by Croasdale (1955: 521, pl. 4: 12) from Alaska. Brook & Williamson (2010: 204) recorded it from Sutherland. John & Williamson (2009: 28) also found it in peaty pools in Ireland. A very rare taxon, seemingly confined to the Arctic, subarctic and north-western Atlantic.
Cell dimensions: L: 230-325 µm; B: 8.5-11 µm; Ap: 5.5-7 µm; L/B: 25-33.
It differs from the nominate variety by being significantly narrower. An acidophile of Sphagnum bogs and moorland peaty pools.

References: 
Brook, A.J. & Williamson, D.B. (2010) A Monograph on some British Desmids.
Croasdale, H.T. (1955) Freshwater algae of Alaska. 1. Some desmids from the interior.
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland.