Phylum: Charophyta   Family: Desmidiaceae

Staurastrum lagerheimii W. Schmidle 1898

A large cell with acute sinuses that are widely open. The semicells are traversely elliptical with a broadly convex apex supporting 8-9 domed or bicuspid teeth. The ventral sides support two large bicuspid teeth. The short processes, with 2-3 concentric rings of teeth, are tipped with 2-3 stout spines. A triradiate species with 4 large intramarginal warts per side when viewed apically.
Named in honour of Nils Gustaf Lagerheim (1860–1926) a Swedish botanist, mycologist, phycologist. It was shortly after moved to a variety of St. anatinum Cooke & Wills 1881 by West & West (1909: 289) with the comment “This variety differs only from typical St. anatinum in the shorter processes, which are scarcely more than half the normal length.” The problem here is what is ‘typical’ St. anatinum? The semicell-shape is far from typical with its broadly convex apex and short processes emanating from just above the median line rather than from the apical angles. It is closer to St. anatinum var. truncatum West 1892, which only seems to differ in having longer processes. However, this taxon has now been synonymised with St. anatinum, along with other varieties, making that species a confused complex. As many of these taxa are only found in the plankton of northern European and Scandinavian lochs and lakes, they are not often encountered. More finds are needed to get a better understanding of the complex.
Overall cell dimensions (2): L: 56-58 µm; B: 82-87 µm.; Is: 17.5-17.9 µm, L/B: 0.65-0.71.
Found in slightly acidic habitats such as in the plankton of lochs, especially at altitude. Rarely recorded in the Outer Hebrides.

References: 
Schmidle, W. (1898). Über einige von Knut Bohlin in Pite Lappmark und Vesterbotten gesammelte Süsswasseralgen.
West, W. & West, G.S. (1909). The phytoplankton of the English Lake district.