Phylum: Charophyta   Family: Desmidiaceae

Staurastrum monticulosum L.A. de Brébisson ex J. Ralfs 1848

First described by Brébisson in Ralfs (1848: 130, pl. 34: 9) and illustrated by Jenner. Mainly found as triradiate cells but occasionally quadriradiate cells are encountered.
Overall cell dimensions: L: 39-57 µm; B: 35-45 µm; Is: 13-19 µm.
A rare desmid in the Outer Hebrides. The species is mainly confined to the Arctic and subarctic. Found in acidic habitats such as moorland pools and bogs.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Ralfs, J. (1848). The British Desmidieae.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.