Phylum: Charophyta   Family: Mesotaeniaceae

Cylindrocystis acanthospora (G. Lagerheim) J. Lütkemüller 1913

First described and illustrated by Lagerheim (1883: 51, pl. 1: 15-17) as Penium acanthosporum. He was uncertain about its taxonomic position and it was later moved to its current position by Lütkemüller (1913: 226). Brook & Williamson (2010: 29, pl. 1: 1-3) make reference to a find by Alan Joyce from Sutherland, Scotland and presumably their unacknowledged drawing is of this find. They also replicate Lagenheim’s drawings of the zygospore. This would appear to be the first record since Lagenheim’s original Swedish find. The cells are subglobose with a single stellate chloroplast with radiating extensions that reach the cell-wall, these are often bifurcate. There is a large central pyrenoid. Cells are larger than the original finds but the main characteristics are the same. There is a natural size-variation in most species, so I’m inclined to leave it here for the time being in the hope that more collections can be located. At this stage I don’t think that varietal status, or describing it as a new species, is necessary.
Brook & Williamson’s cell dimensions: L: 15-18.5 µm; B: 12-13.5 µm.
Isle of Lewis cell dimensions: L: 20.5-21.7 µm; B: 17.9-20.6 µm; L/B: 1.06-1.15.
The Isle of Lewis sample came from mosses on wet rocks with a slightly acidic pH.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Lagerheim, G. (1883). Bidrag till Sveriges algflora.
Lütkemüller, J. (1913). Die Gattungen Cylindrocystis Menegh.