Phylum: Charophyta   Family: Mesotaeniaceae

Roya obtusa (Brébisson) West & G.S. West 1896

West & West (1896: p.152, pl.3: 23-24 [as var. montana, now regarded as a synonym]) found it abundant on dripping rocks in Yorkshire and Cumbria. It was named in honour of Dr. John Roy, who was the first to point out the differences between this species and the genus Closterium. It is rarely recorded in the Outer Hebrides.

References: 
West, W. & West, G.S. (1896) On some new and interesting freshwater algae.
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands.
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland.