Phylum: Charophyta   Family: Desmidiaceae

Euastrum gemmatum  J. Ralfs 1847

Of the European species, only E. germanicum and E. spinulosum are similar. E. gemmatum differs from these primarily in the three basal swellings and the almost rectangular lower part of the semicells. This is a most variable species both in terms of the extent and shape of the lateral lobes but also in the outer protuberances, which can sometimes be only partly produced. Of the illustrations in the literature, the Lewis, Outer Hebrides cells closely resemble those depicted by G.M. Smith (1924: 26, pl. 57: 1-2).
Cell dimensions: L: 58.2-60.6 µm; B: 40.4-40.9 µm; Is: 11.3-11.8 µm; Th: 28.3-30.1 µm; L/B: 1.44-1.49.
West & West (1905: 64) note: “It is widely distributed, but somewhat scarce.” 120 years later, it is rare. Recent finds have been in slightly acidic vegetated loch-margins.

References: 
Ruzicka, J. (1981). Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
Smith, G.M. (1924). Phytoplankton of the Inland Lakes of Wisconsin: Part II Desmidiaceae.
West, W. & West, G.S. (1905). A Monograph of the British Desmidiaceae, Volume 2.