Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus robustus (E. Messikommer) P.F.M. Coesel & K.J Meesters 2023

First described and illustrated by Messikommer (1928: 208, pl. 8: 11) as Staurastrum cuspidatum var. robustum. Recently, it was raised to species rank by Coesel & Meesters (2023: 205, pl. 99: 25-26) mainly on the results of scanning electron microscopy, which revealed essential differences in the cell sculpturing.
Cell dimensions: L: 24-30 µm; B: 22-27 µm; Is: 6.5-7.6 µm; Sp: 1.4-4.1 µm; Overall B: 28-34.
This species is proving to be quite scarce in the Outer Hebrides. It occurs in mildly acidic water such as small lochs. Interestingly, it has been found with moss on wet rocks.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition).. Desmids of the Lowlands.
Messikommer, E. (1928).. Beitrage zur Kenntnis der Algenflora des Kantons Zurich, III: Die Algenvegetation der Hinwiler- unde Oberhöflerriedes.