Phylum: Charophyta   Family: Desmidiaceae

Micrasterias thomasiana W. Archer 1862

First described and illustrated by Archer (1862: 239, pl. 12: 1-10). West & West (1905: 112) note: “This species, which in its type form is so characteristic, is one of the most variable in the genus. The relative size of the basal projections, and the number and disposition of the surface-teeth are very variable, and it is sometimes difficult to obtain two individuals which agree in these respects.” Named in honour of Mrs. Herbert Thomas who authored papers on Cosmaria.
Cell dimensions: L: 200-260 µm; B: 170-230 µm; Is: 21-31 µm; L/B: 1.10-1.30.
Found in acidic mesotrophic waters such as moorland pools and abandoned peat-cuttings, but rarely encountered.

References: 
Archer, W. (1862) Description of a new species of Micrasterias (Ag. et Aliorum, non Ehr.), with remarks on the distinctions between Micrasterias rotata (Ralfs) and M. denticulata (Bréb.).
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ruzicka, J. (1981) Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2.