Cosmarium amstelodamense Van Geest et Coesel, 2019

Geest, Alfred Van & Coesel, Peter, 2019, Some new and interesting desmids (Streptophyta, Desmidiales) from ephemeral puddles in the urban and industrial areas of Amsterdam (Netherlands), Phytotaxa 387 (2), pp. 119-128 : 125

Cosmarium amstelodamense Van Geest et Coesel sp. nov. (Figs. 4, 10, 22)

Diagnosis: Cells 1.2–1.3 times longer than broad, with a moderately deep constriction. Sinus linear, closed for the greater part. Semicells in frontal view subcirculair with a slightly flattened apex. Each semicell with 16, almost equally sized marginal crenations. Cell wall ornamentation consisting of 3–4 concentric series of submarginal rounded verrucae as well as 2–3 irregular, transversal rows of granules or short costae just above the isthmus. In between the submarginal and the supraisthmial ornamentation the cell wall is unsculptured. Cells in lateral view elliptic with a shallow, widely open, median invagination. Semicells in lateral view somewhat ovoid with a slight, basal inflation about 1/3 distance from the median invagination. Semicells in apical view ellipsoid with broadly rounded poles and a slight median inflation. Chloroplast with a single, central pyrenoid. Dimensions: cell length 32–37 μm, cell breadth 23–26μm, cell thickness 18–19μm, breadth of isthmus 12–14μm.

Type:— THE NETHERLANDS. Amsterdam: rain puddle, 52.38525 N, 4.90167 E, Van Geest , 31 May 2016 (holotype L! Nationaal Herbarium Nederland, Hugo de Vries Lab. no 2018.07, preserved as a fixed natural sample).

Etymology: The name ‘amstelodamense’ is a Latinization of Amsterdam, being our collection area.

Because of the combination of a crenate cell outline with transversal series of supraisthmial granules, this species should be compared with species such as C. speciosum P. Lundell , C. subspeciosum Nordstedt , C. costatum Nordstedt , C. cinctutum Nordstedt , etc., species of which quite a series of infraspecific taxa have been described. Our alga, readily to be recognized by the regularly wrinkled, subcircular outline of the semicells, could not be matched with any known species in a satisfactory way. All of the above-mentioned taxa are characterized by a semi-elliptic to pyramidal outline of the semicell, not a subcircular one. As our alga was found to be but little variable in shape and occurred in six out of the nine localities sampled (1, 2, 3, 4, 5 and 8), we think it justified to describe it as a new species.