Phylum: Charophyta   Family: Desmidiaceae

Staurastrum pachyrhynchum C.F.O. Nordstedt 1875

First described and illustrated by Nordstedt (1875: 32, pl. 8: 34). Similar to the smaller Staurastrum sibiricum, especially the biradiate form.
Cell dimensions: L: 22-45 µm; B: 22-45 µm; Is: 8-15 µm.
An Arctic-boreal species of acidic conditions. Status largely unknown in the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Nordstedt, C.F.O. (1875). Desmidiae arctoae.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.