Phylum: Charophyta Family: Desmidiaceae
Staurastrum pungens L.A. de Brébisson ex J. Ralfs 1848
First described by Brébisson in Ralfs (1848: 130, pl. 34: 10) and illustrated by Jenner. The cell-wall is finely granulate, best seen in empty cells.
Overall cell dimensions: L: 24-50 µm; B: 22-44 µm; Is: 8-10 µm.
This would seem to be genuinely rare with few records for the Outer Hebrides. An acidophile found in abandoned peat-cuttings and moorland pools and bogs.
References:
Coesel, P.F.M. & Meesters, K.J. (2013).. European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Ralfs, J. (1848).. The British Desmidieae.
West, W., West, G.S. & Carter, N. (1923).. A Monograph of the British Desmidiaceae, Volume 5.