Euastrum dubioides 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 : 107-108

Euastrum dubioides Van Westen et Coesel spec. nov. ( Figs 5 , 9, 10 , 31 ).

Diagnosis: Cells 1.4 times longer than broad, with a deep median constriction. Sinus linear, closed for the greater part. Semicells in frontal view composed of a rectangular-trapezoid basal part and a much narrower, rectangular apical part. Apices truncate with a rather deep, narrow, median invagination. Apical angles furnished with a blunt granule. Lateral and basal lobes rounded, the lateral ones furnished with a single, the basal ones with two blunt marginal granules. Marginal granules in radial series with a number of intramarginal ones. Semicells with a slight central inflation furnished with some four granules arranged in a square. Semicells in apical view elliptic, with central inflation. Chloroplast with a single, central pyrenoid. Dimensions: cell length 25–29 µm, cell breadth 17.5–21 µm, breadth of apex 10.5–13 µm, cell thickness 12–13 µm, isthmus 5–7 µm.

Type:— THE NETHERLANDS. Drenthe: wet meadow with Juncus effusus in estate Eexterveld near Eext, 53.014058° N, 6.695333° E, between mosses and filamentous algae. Van Westen, 1 April 2011 (holotype L! Hugo de Vries Lab 2019.01, preserved as a fixed natural sample).

Differential diagnosis:—At first glance, the above-described alga reminds of Euastrum dubium Nägeli , especially its var. ornatum Woloszynska. However , where semicells in Eu. dubium are characterized by gradually converging lateral sides with a distinct curve midway ( Figs 32, 33 ), semicells in our alga are partitioned into a more or less rectangular basal part abruptly passing into a much narrower, rectangular apical part. In that feature it also differs from Eu. denticulatum F.Gay which species moreover is characterized by a lower cell length to breadth ratio and less pronounced lateral lobes ( Fig 34 ).

Actually, in rough cell outline our alga could be rather compared with Eu. insulare (Wittrock) Roy. However , Eu. insulare is characterized by a wide, very shallow median apical indentation and is in want of any marked cell wall ornamentation. Therefore we think it justified to describe our alga as a new species.

In the province of Drenthe, Euastrum dubioides is found mainly in wet meadows between mosses and in slightly acidic oligo-mesotrophic shallow pools dug for nature restoration purposes.

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.