Phylum: Charophyta   Family: Desmidiaceae

Staurastrum verticillatum W. Archer 1869

First described and exhibited by Archer (1869: 196) to members of the Dublin Microscopical Club. He commented: “… remarkable for being probably the very largest of rayed or armed forms yet found in Europe, …” This is similar to Staurastrum ophiura Lundell 1871, found just two years later. Archer’s find is quite a bit larger and has more pronounced granules at the base of the semicells. St. ophiura usually has a whorl of verrucae when viewed apically, which are said to be lacking in St. verticillatum. However, the Isle of Lewis specimens have pronounced verrucae. Cell dimensions: L: 81-90 µm; B: 41-45 µm.; Is: 21-24.2 µm; Overall LxB: 90-122 x 143-149 µm.
An Atlantic distribution only known with certainty from Scotland and Ireland. West, West & Carter (1923: 155) only mention two sites for Scotland, one of these is Loch Mor Bharabhais, Isle of Lewis, Outer Hebrides. Found in acidic, mesotrophic, lochs and bogs; extremely rare.

References: 
Archer, W. (1869). [In] Dublin Microscopical Club [In] Proceedings of Societies.
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Lundell, P.M. (1871). De Desmidiaceis, quae in Suecia inventae sunt, observationes criticae.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.