Cosmarium neonotabile Van Westen & Coesel 2021, spec. nov.
Creators: name: Van Westen, Marien C.
name: Coesel, Peter F. M.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Plantae
Charophyta
Conjugatophyceae
Zygnematales
Desmidiaceae
Cosmarium
Cosmarium neonotabile

description: Cosmarium neonotabile Van Westen & Coesel spec. nov. (Figs 3, 4, 15, 16, 17, 32)   
Diagnosis: Cells 1.4-1.6 times longer than broad with a shallow, linear sinus closed or narrowly open for the greater part. Semicells in frontal view trapeziform-oblong with slightly convex lateral sides and a truncate apex. Each semicell with 12-14 marginal crenations/undulations, those at the apex less deep than those on the lateral sides. Cell wall ornamentation consisting of 2-3 intramarginal, concentric series of flattened verrucae corresponding with the marginal crenations. Just above the isthmus sometimes another series of most flattened, hardly visible granules. Lateral cell view elliptic with a shallow, obtusely angled constriction. Apical view elliptic. Chloroplast with a single, central pyrenoid. Dimensions: cell length 22–31 µm, breadth 16–23 µm, L/B= 1.35–1.6, thickness about 15 µm, isthmus 10–13 µm.  
Type:— THE NETHERLANDS. Province of Noord-Holland in estate Laegieskamp near Bussum, 52.278072 ° N, 5.138113° E. Van Westen, 5 September 2020 (holotype L! Hugo de Vries Lab 2021.02, preserved as a fixed natural sample and represented by our fig. 3).  
 Differential diagnosis:—The above-diagnosed taxon much resembles C. notabile Brébisson as depicted in the flora by West & West (1908, pl. 66: 15). However, the original illustration of C. notabile by De Brébisson (1856, pl. 1: 15) shows cells with a higher number of marginal crenations (14–16 per semicell) and, more essentially, a distinctly narrower cell isthmus. Whereas isthmus to cell breadth ratio in our alga under discussion equals 0.55–0.64, that in De Brébisson’s one equals 0.4. For that matter, it has to be noticed that the intramarginal series of verrucae in our C. neonotabile may be flattened to such an extent that they are easily overlooked. That might explain the fact that West & West (1908: 16) designate C. notabile as ‘smooth-walled’.   
 Unfortunately, De Bary (1858, pl. 6: 52–54) under the name of C. notabile Brébisson depicted an alga most probably relating to C. benedictum Ducellier (Van Geest & Coesel, 2019). As De Bary’s concept of C. notabile was adopted in the flora by West & West (1908, p. 15), a lot of confusion was to be expected in later publications. It was only Croasdale (in Prescott et al. 1981: 173) who emphasized the difference in concept of C. notabile between De Breìbisson (1856) and De Bary (1858). She rightly recognizes the need of a new name for the many (seemingly?) smooth-walled forms figuring in desmid literature under the name of C. notabile and newly describes C. levinotabile to meet that need. Unfortunately, as holotype of that species she mentions figs 6: 1–5 of C. notabile in De Bary (must be 6: 52–54) and as iconotypes figs 198: 1–5 in Prescott et al. (1981) representing both the drawings of C. notabile in De Bary and drawings of C. notabile in the flora by West & West (1908) in our opinion representing distinctly different species. Consequently, Croasdale’s description of C. levinotabile should be considered to be invalid.   
 Next to the trapeziform semicell shape rendered by our type material of C. neonotabile (figs 3, 15 and 17) elsewhere in the Netherlands we encountered populations with predominantly semi-oblong semicells (figs 4, 16 and 32). That latter form largely matches C. cedercreutzii Grönblad (1921, p. 27, pl. 6: 12-13) but is to be distinguished by much deeper marginal crenations. As the two cell forms found in our Dutch material appeared to be mutually connected by transitional forms we concluded to deal with one and the same species.
description: Published as part of 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, pp. 240-248 in Phytotaxa 522 (3) on pages 244-246, DOI: 10.11646/phytotaxa.522.3.7, http://zenodo.org/record/5560451