Phylum: Charophyta Family: Desmidiaceae
Euastrum dubium C. Nägeli 1847
Semicells roughly trapeziform, sinus deep and closed for the most part. Basal angles broadly rounded and often geminate. Lateral lobes broadly rounded producing deeply curved incisions. Apices truncate with a deep, partly open, median incision. Apical angle usually with a papilla. Empty cells show a slight central protuberance and some granulation around the periphery.
Cell dimensions: L: 34.0-38.6 µm; B: 21.7-23.7 µm; B-apex: 13.0-15.4 µm; Is: 6.1-8.0 µm; Th: 12-17 µm; L/B: 1.50-1.76.
Common in acidic conditions such as peaty lochs and bogs, but easily confused with similar species, especially where no side view is on show or empty cells.
References:
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Nägeli, C. (1849) Gattungen einzelliger Algen, physiologisch und systematisch bearbeitet.
Ruzicka, J. (1981) Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2.