Phylum: Charopyta Family: Desmidiaceae
Staurodesmus extensus var. joshuae (Gutwinski) Teiling
Differs from the nominate in having longer spines which are either parallel or convergent. Found in acidic moorland pools and Sphagnum bogs. The scarcest of the varieties and of unknown status in the Outer Hebrides
References:
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
Teiling, E. (1967) The desmid genus Staurodesmus. A taxonomic study