Phylum: Charophyta   Family: Desmidiaceae

Staurastrum hibernicum W. West 1892

Since West (1892: 177, pl. 23: 6) named and illustrated this species, West & West (1912: 156, pl. 124: 5-9) subsequently regarded it as a variety of Staurastrum orbiculare and note: "This is the largest form of St. orbiculare and is principally characterized by the more pronounced basal angles of the semicells and the flattened apices." It has since been returned to its original designation.
Cell dimensions: L. 42-65 µm, B. 36-56 µm, Is. 10-20 µm.
West & West (l.c.) give no records for Scotland. It was first recorded in the Outer Hebrides in 2020 from a drainage ditch in a conifer plantation. Undoubtedly rare.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
West, W. (1892). A contribution to the freshwater algae of west Ireland.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.