Phylum: Charophyta   Family: Desmidiaceae

Staurastrum cornutum W. Archer 1881

An extremely rare arctic-alpine species found in the tychoplankton of oligotrophic waters such as lochans and moorland pools. Distribution unknown for the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5