Phylum: Charophyta   Family: Desmidiaceae

Cosmarium tasiussaqense R. Lenzenweger 1989

Cells small, about as long as broad, the sinus has a dilate apex, then linear and closed for 60 percent of its length before opening widely. Semicells are trapeziform with broadly rounded basal angles. Each upper lateral angle is punctuated with four widely-spaced intramarginal granules, starting at the apical angle and finishing below the median line, giving an undulate outline. There would also appear to be a secondary series of granules running parallel (seen best in empty cells). The apex is smooth and slightly convex. Empty cells in face view show a series of fairly random pores. The broadest point of the semicells is close to the median line. Side view is orbicular; apical view is elliptic with slight side tumidity. Also in apical view, the eight intramarginal granules as seen in face view, are replicated on each side. Chloroplast axile with one central pyrenoid. Zygospore unknown.
Cell dimensions: L. 21.6-24.3 µm; B. 21.2-23.1 µm; Is. 6.2-7.5 µm; Th. 12.3-14.3µm; L./B. 0.96-1.11.
R. Lenzenweger (1989: 105) doesn’t make reference to other taxa for comparison, and for habitat he records: zona ripae lacus. Unfortunately, there is no mention of the flora (aquatics) or the pH. Lenzenweger’s drawing (l.c., pl. 2: 27) clearly shows the four intramarginal granules and a parallel series within, also the convex apex.
C. tasiussaqense is named after the discovery site: Tasiusaq (modern spelling), located on Tasiusaq Island within Upernavik Archipelago, a vast collection of small islands on the west coast of Greenland facing Baffin Bay. This original find occurred in the realm of the Nearctic. The South Uist find is the second record worldwide and the first for the western Palearctic.
The only taxon showing any similarity is C. lapponicum O. Borge (1913: 19, pl. 1: 14). This is smaller than C. tasiussaqense with virtually no overlap in size. It has a truncate apex and minute intramarginal granules: these granules are variable in number and position. Indeed, Borge (l.c., pl. 1: 15) describes C. lapponicum var. undulatum with slightly more undulate side, but later finds showed intermediates between the two; therefore, it is generally regarded as synonymous. This is another rare species with a seemingly Arctic-alpine distribution.

References: 
Borge, O. (1913) Beiträge zur Algenflora von Schweden, II. Die Algenflora um den Torne-Trask-see in Schwedisch-Lappland.
Lenzenweger, R. (1989) Zieralgen von Süd-Grönland.