Phylum: Charophyta   Family: Desmidiaceae

Xanthidium cristatum var. uncinatum Brébisson ex Ralfs 1848

Found in oligotrophic lochs and lochans, also in peaty pools. Roy & Bisset (in West & West 1912) give common for Sutherland but make no mention of the Outer Hebrides. It would seem to been quite scarce. "Differs from the nominate variety by larger cells and in that the spines are curved upwards." (Coesel & Meesters 2013).

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