Phylum: Charophyta   Family: Desmidiaceae

Staurastrum muticum Brébisson ex Ralfs 1848

Regarded as widespread in nutrient-poor ponds and bogs and vegetated loch-margins. It exhibits quite a size range for a small desmid. Proving to be quite scarce in the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus.
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles.
West, W. & West, G.S. (1912) A Monograph of the British Desmidiaceae, Volume 4.