Phylum: Charophyta   Family: Desmidiaceae

Staurastrum sibiricum O. Borge

Described as an acidophile, but possibly more tolerant of circumneutral waters. A rare arctic species of little known distribution in Scotland

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
Prescott, W.G., et al. (2001 reprint) A Synopsis of North American Desmids. Part II, Desmidiaceae: Placodermae, Section 4