Phylum: Charophyta   Family: Closteriaceae

Closterium ralfsii J. Ralfs 1848

First described in Ralfs (1848: 174, pl. 30: 2). West & West (1904: 182, pl. 24: 6-7) comment: “The type of Cl. ralfsii is one of the rarest and most striking of British Closteria.” The variety hybridum only differs in being less tumid but determination is often difficult as the cell dimensions overlap considerably.
Cell dimensions: L: 534-554 µm; B: 48-52 µm; Ap: c.8 µm; L/B: 10-12.
An acidophile, rarely recorded.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Ralfs, J. (1848). The British Desmidieae.
West, W. & West, G.S. (1904). A Monograph of the British Desmidiaceae, Volume 1.