Cosmarium logiensiforme Van Westen et Coesel, 2020

Van Westen, Marien C. & Coesel, Peter F. M., 2020, Taxonomic notes on desmids from the Netherlands III, with a description of five new species, Phytotaxa 443 (1), pp. 107-115 : 113

Cosmarium logiensiforme Van Westen et Coesel spec. nov. ( Figs 1 , 20, 21, 22 , 28 )

Diagnosis: cells 1.3-1.4 times longer than broad, with a deep, linear constriction. Sinus narrowly linear with a dilated extremity. Semicells in frontal view trapeziform to semi-elliptic with broadly rounded basal angles. Cell wall furnished with evenly distributed granules. Semicells in lateral view about circular, in apical view broadly elliptic. Chloroplast with two pyrenoids. Dimensions: cell length 33-41 µm, cell breadth 25-30 µm, cell thickness 17-20 µm, isthmus 10–12 µm.

Type:— THE NETHERLANDS. Limburg: shallow pool in estate De Hamert, near Wellerlooi, 51.531886° N, 6.183763° E, between Sphagnum and Utricularia minor , pH 4.0 and conductivity 383 µS cm-1. Van Westen, 16 June 2018 (holotype L! Hugo de Vries Lab 2019.04, preserved as a fixed natural sample)

Differential diagnosis:— C. logiensiforme resembles C. logiense Bisset as described in the well-known flora by West & West (1908: 163, pl. 80: 1-2). However, cell dimensions in our alga are almost twice as small as those in C. logiense and there is also a difference in the pattern of cell wall granules. Where in West & West (l.c.) there is talk of granules that are densely arranged in obliquely decussating and vertical series, granules in C. logiensiforme are evenly distributed without showing any special pattern. For that matter, it has to be remarked that the original description of C. logiense by Bisset (1884: 194, pl. 5: 4) does not indicate the above-mentioned pattern of granulation, neither in the diagnosis nor in the accompanying figure. Moreover, cell dimensions are larger and semicells are more reniform than those represented in West & West (l.c.) so it is questionable whether one and the same species is at issue.

Anyhow, it should be clear that our alga under discussion, despite a rough similarity, represents another species than C. logiense either in the original description by Bisset (1884) or in the concept by West & West (1908).

The type material of C. logiensiforme originates from an acidic, mesotrophic moorland pool in the Dutch province of Limburg but the species in question was already found earlier in nature reserve ‘De Teut’ (in adjacent Belgium) where it occurred rather abundantly in oligotrophic bog pools.

Figures

FIGURES 1–6. Drawings 1. Cosmarium logiensiforme. 2. C. mandosii. 3. C. arcuatiporosum (with zygospore). 4. Euastrum tumoriferum. 5. Eu. dubioides. 6. Eu. neogutwinskii (with zygospore).

FIGURES 16–25. LM photographs. 16–19. Cosmarium arcuatiporosum (19. zygospore). 20–22. C. logiensiforme. 23-25. C. mandosii. Scale bar = 10 µm.

FIGURES 26–34. SEM photographs. 26. Cosmarium mandosii. 27. C. arcuatiporosum. 28. C. logiensiforme. 29. Euastrum tumoriferum. 30 Eu. neogutwinskii. 31.Eu. dubioides. 32. Eu. dubium var. dubium. 33 Eu. dubium var. ornatum. 34. Eu. denticulatum. Scale bar = 10 µm.