Phylum: Charophyta   Family: Desmidiaceae

Staurastrum vestitum J. Ralfs 1848

A medium-sized cell with an open sinus. Semicells subfusiform with the apex slightly convex with about six emarginate granules. There are two subapical bifurcate spines. In apical view these two bifurcate spines show prominently. West, West & Carter (1023: 158) give overall dimensions of LxB: 28-43 x 46-90 µm. They also describe a variety subanatinum, which differs only in being broader, up to 102 µm in breadth. They named it because of its similarity with St. anatinum in face-view. Strangely, Coesel & Meesters (2013: 63) made this a variety of St. anatinum, seemingly overlooking the fundamental diagnostic feature being the two bifurcate subapical spines. All the cells found in the Outer Hebrides fall within the parameters set by West, West & Carter for the nominate variety. I would suggest cells broader than 90 µm are rare and barely justify varietal status.
Overall cell dimensions: L: 33-42 µm; B: 50-78 µm.; Is: 10.6-13 µm, L/B: 0.48-0.68.
Found in slightly acidic habitats such as in the plankton of lochs, especially at altitude. It has also been found in moorland pools with Sphagnum. In such habitats it’s not uncommon in the Outer Hebrides.

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