Phylum: Charophyta   Family: Closteriaceae

Closterium juncidum var. robustius A.I. Lobik 1915

First described by Lobik (1915: 325) without illustration. He notes: “The thickness of the ends is quite constant in all cases, namely, 5-5.5 µm. The shell is colored, striated, 5 striations are visible at a time; each half-cell has 6 pyrenoids.” Brook & Williamson (2010: 223) maintain it as a separate taxon but reduce it to a forma (?). A year later, Brook, Williamson & John, in John et al. (2011: 627) synonymize vars. brevius, elongatum & robustius without further comment. They then give considerable cell dimensions for Cl. juncidum of L: 90-630 x B: 6-15 suggesting a species complex.
Cells from the Outer Hebrides show 4-5 striae (costae) in face view. Not mentioned by Lobik or other authors, is that a distinct apical pore is visible. I therefore maintain the variety and would suggest it might well jusify being described as a full species.
Cell dimensions: L: 210-275 µm; B: 8.8-9.6 µm; Ap: 4.4-4.9 µm; L/B: 22-31.
Rarely encountered in acidic oligotrophic moorland pools and peaty bogs.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition). The Freshwater Algal Flora of the British Isles.
Lobik, A.I. (1915). Note sur les desmidiacées récoltées par M. Perfiliev aux environs de Sestroretsk (gouv. Petrograd).