Phylum: Charophyta   Family: Desmidiaceae

Staurastrum controversum var. semivestitum (W. West) P.F.M. Coesel 1996

First described and illustrated by West (1892: 732, pl. 9: 38) as Staurastrum vestitum var. semivestitum. More recently, it was moved to its current position by Coesel (1996: 20, fig. 11). It differs from the nominate variety with the processes parallel to slightly divergent. Records seem to show that it’s also slightly smaller.
Cell dimensions: L. 20-31 µm, B. 34-50 µm, Is. 7-12 µm.
Found in similar habitats to the nominate variety and equally rare.

References: 
Coesel, P.F.M. (1996). Taxonomic notes on Dutch desmids III.
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
West, W. (1892). Algae of the English Lake District.