Phylum: Charophyta   Family: Desmidiaceae

Actinotaenium americanum (W. West & G.S. West) P.F.M. Coesel & K.L. Meesters 2023

Originally described by West & West (1898: 281, pl. 18: 5-6) as Cylindrocystis americana, it was later moved by Teiling (1954: 413, fig. 75) to Actinotaenium diplosporum var. americanum based on its chloroplast structure. Coesel & Meesters (2023) raised it to species rank without comment. Cells ellipsoidal with the lateral sides slightly converging towards the rounded apex. Chloroplast lobostelloid with one pyrenoid.
Cell dimensions: L: 52-65; B: 22-26; L/B: 2.20-2.60.
An acidophile of moorland bogs and dripping rocks. Status unclear for the Outer Hebrides but probably not uncommon.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ruzicka, J. (1981) Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
Teiling, E. (1954) Actinotaenium, genus Desmidiacearum resuscitatum.
West, W. & West, G.S. (1898) On some Desmids of the United States.