Euastrum tumoriferum (Kossinskaja) 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 : 112

Euastrum tumoriferum (Kossinskaja) Van Westen et Coesel stat. nov. ( Figs 4 , 7, 8 , 29 ).

Basionym: Euastrum binale forma tumoriferum Kossinskaja 1936, p. 417 , pl. 1: 10.

Kossinskaja (l.c.), in her diagnosis of forma tumoriferum mentions a central tumour as well as 3-crenate lateral lobes as differentiating features with respect to the nominate forma of Eu. binale . She also compared her newly described forma with Eu. binale forma gutwinskii , from which it could be distinguished not only by the big central tumour but also by narrower apical lobes (relative to the breadth of the semicell base).

Remarkably, in Croasdale (1955: 530) there is talk of Eu. binale var. tumoriferum Kossinskaja without a formal raise in rank from forma to variety.Also Grönblad (1963: 21) incorrectly makes mention of Eu. binale var. tumoriferum Kossinskaja.

For that matter, considering illustrations in desmid literature, the taxon under discussion several times also has been labeled Euastrum binale var. gutwinskii (Schmidle) Homfeld , see e.g. Dick (1919, fig. 11), Messikommer (1942, pl. 4: 2) and Coesel & Meesters (2007, pl. 48: 7). Yet we are of opinion that we have to do with a well distinguishable taxon. As we tend to get rid of infraspecific taxa in desmid taxonomy ( Van Westen & Coesel 2018) we herewith raise Euastrum binale forma tumoriferum Kossinskaja to a separate species. The main differentiating feature with respect to Eu. neogutwinskii is in the breadth of the semicell apex (without possible papillae) relative to the total semicell breadth, viz. lower than 0.60 in Eu. tumoriferum versus higher than 0.65 in Eu. neogutwinskii , resulting in a more pyramidal outline of the semicell in Eu.. tumoriferum compared with that in Eu. neogutwinskii . A SEM picture of Eu. tumoriferum ( Fig. 29 ) revealed some conspicuous shallow scrobicles near the basal lobes, a feature that we never observed in Eu. neogutwinskii . Moreover, the number of small scrobicles around the central inflation is much lower than that in Eu. neogutwinskii ( Fig. 30 ), compare also Coesel (2009). So, presumably this is an additional discriminating character of Eu. tumoriferum .

As far as could be traced, Eu. tumoriferum is of rather rare occurrence in colder regions of Europe and North America. We encountered it recently in the Dutch province of Overijssel, in the wetlands of ‘Kiersche Wijde’. This location is close to the Dutch province of Drenthe, a province marked by a relatively cold climate where several arcticalpine desmid species were found before ( Van Westen 2015). As compared to Eu. neogutwinskii there is probably also a difference in ecology. Whereas in the Netherlands Eu. neogutwinskii is most common in distinctly acidic bogs and moorland pools, Eu. tumoriferum so far was only encountered in slightly acidic fen habitats.

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 7–15. LM photographs. 7, 8. Euastrum tumoriferum. 9, 10. Eu. dubioides. 11–15. Eu. neogutwinskii (14, 15 zygospore). 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.