Cosmarium sphagnicoliforme Van Westen & Coesel, 2021

Van Westen, Marien C. & Coesel, Peter F. M., 2021, Taxonomic notes on desmids from the Netherlands IV, with a description of another five new species, Phytotaxa 522 (3), pp. 240-248 : 247

Cosmarium sphagnicoliforme Van Westen & Coesel spec. nov. ( Figs 7 , 27, 28, 29 , 35 )

Diagnosis: Cells a little bit broader than long with a rather shallow, U-shaped, open sinus. Semicells in frontal view more or less hexagonal, the lateral angles variously pronounced, the basal angles sometimes papillate. Cell wall furnished with two blunt, asymmetrically disposed granules: one in the upper right angle close to the apical margin, the other one in the left part of the semicell approximating the lateral angle. Semicells in lateral view about globose, in apical view elliptical with a papilla on each side near the somewhat attenuate poles. Zygospores irregularly elliptical-oblong, smooth-walled. Chloroplast with a single, central pyrenoid. Dimensions: cell length 6.5–9.5 µm, breadth 6.5–10 µm, thickness about 5 µm, isthmus 4.5–5.5 µm, zygospore (fig. 29) somewhat irregularly oblong, 13 x 10 µm.

Type:— THE NETHERLANDS. Drenthe: rain puddle on loamy sand in estate De Haar near Assen, 52.942598° N, 6.519883° E, pH 7.9 conductivity 11 µS cm- 1. Van Westen, 8 August 2015 (holotype L! Hugo de Vries Lab 2021.04, preserved as a fixed natural sample and represented by our fig. 7) .

Differential diagnosis:— C. sphagnicoliforme much resembles C. sphagnicola . Mean cell dimensions are a little bit smaller but the main difference is in the outline of the semicell when seen in frontal view. Whereas in C. sphagnicola semicells are widest near the apex, those in C. sphagnicoliforme are widest in their basal part including the lateral angles. Next to those morphological differences we could assess also a possible difference in ecology: whereas C. sphagnicola is characteristic of acidic Sphagnum vegetation, C. sphagnicoliforme was encountered in shallow rain puddles on loamy substrates.

Because of the close resemblance to C. sphagnicola confusion with that species in desmid literature is likely. For instance, when consulting the flora by Coesel & Meesters (2007), we now have to conclude that the C. sphagnicola labeled cell depicted on pl. 69: 12 refers to that species indeed, but those on pl. 69: 10–11 better be identified as C. sphagnicoliforme .

Figures

FIGURES 1–8. Drawings 1. Cosmarium grantii (from Eexterveld, province of Drenthe, the Netherlands). 2. C. palatiniforme. 3, 4. C. neonotabile (no 4 from Holmers, province of Drenthe, the Netherlands). 5. C. neocrenatum. 6. C. sphagnicola. 7. C. sphagnicoliforme (with zygospore). 8. C. regnesiforme.

FIGURES 24–29. LM photographs. 24–26. Cosmarium sphagnicola (from Nolderveld, province of Drenthe, the Netherlands). 27–29. C. sphagnicoliforme (from type location) (29. zygospore). Scale bar = 10 µm

FIGURES 30–38. SEM photographs. 30. Cosmarium grantii (from Eexterveld). 31. C. neocrenatum (from Iceland). 32. C. neonotabile (from Holmers). 33. C. palatiniforme (from type location). 34. C. sphagnicola (from Eexterveld). 35. C. sphagnicoliforme (from type location). 36, 37. C. regnesiforme (from type location). 38. C. regnesi (Zeijen, province of Drenthe, the Netherlands). Figures 30–33: Scale bar = 10 µm, Figures 34–38: Scale bar = 5 µm