Phylum: Charophyta   Family: Desmidiaceae

Staurastrum ralfsii (West & G.S. West) Coesel & Meesters 2013

West & West (1912: p. 156, pl. 124: 10-11, as a variety of St. orbiculare) describe it as "abundant and widely distributed". This is still the situation in the Outer Hebrides. An acidophile of loch-margins and boggy pools.

References: 
West, W. & West, G.S. (1912) A Monograph of the British Desmidiaceae, Volume 4.
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus.