Phylum: Charophyta   Family: Desmidiaceae

Staurastrum monticulosum Brébisson

An acidophile of mainly Arctic and boreal regions. Probably rare in the Outer Hebrides. The Benbecula (NF8392 4796) sample had many quadriradiate cells which tend to give a great length/breadth ratio

References: 
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
Carter, C.F. & Williamson, D.B. (2018) A contribution to the desmid (Charophyta, Conjugatophyta) flora of Newfoundland