Phylum: Charophyta   Family: Desmidiaceae

Pleurotaenium nodosum (J. Ralfs) P.M. Lundell 1871

First described and illustrated in Ralfs (1848: 218, pl. 35: 8) as Docidium nodosum. Later moved by Lundell (1871: 90) to Pleurotaenium. West & West (1904: 214) describe it well: “Cells large or moderately large, 6.5-8 times longer than their diameter; semicells with nodulose margins, cause by four rings of prominent nodules, one basal ring, and three other equidistant rings, 6-8 nodules in each ring, gradually tapering from base to apex; …”
Cell dimensions: L: 280-520 µm; B: 40-80 µm; L/B: 6-8.
Found in mildly acidic habitats such as moorland pools and bogs, also in shallow loch-margins. A rare species.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Lundell, P.M. (1871) De Desmidiaceis, quae in Suecia inventae sunt, observationes criticae.
Ralfs, J. (1848) The British Desmidieae.
Ruzicka, J. (1977) Die Desmidiaceen Mitteleuropas, Volume 1, Part 1.
West, W. & West, G.S. (1904) A Monograph of the British Desmidiaceae, Volume 1.