Cosmarium spierense Van Westen et Coesel, 2018

Van Westen, Marien C. & Coesel, Peter F. M., 2018, Taxonomic notes on desmids from the Netherlands II, with a description of six new species, Phytotaxa 385 (1), pp. 1-12 : 6-8

Cosmarium spierense Van Westen et Coesel sp. nov ( Figs 7–8 , 27–40 )

Cells slightly longer than broad to about as long as broad, deeply constricted; sinus linear and closed for the most part. Semicells in frontal view suboblong with broadly rounded angles and convex lateral sides. Lateral sides, including the apical angles, 5–6-crenate, the crenations near the basal angle with one granule, the other ones generally with two granules. Apex truncate and bi-undulate. Cell wall ornamented with small granules, arranged in short, intramarginal, radiating series, the upper 4–5 lateral series doubled near the margin. In addition, a central tumour ornamented with 6 bended vertical series of granules, the inner two as a rule mutually fused to a big, central wrath. Semicells in apical view broadly elliptic with a more or less triangular tumour on either side, in lateral view subovate with a faint inflation near the base. Chloroplast axile with one pyrenoid. Zygospore globose, furnished with long, stout, furcate spines.

Dimensions: cell length 24–31 μm, breath 22–28 μm, thickness 17–18 μm, isthmus 8.7–10.5 μm; L/B 1.07–1.14. Zygospore diameter (exclusive of spines) about 30 μm.

Type:— THE NETHERLANDS. Drenthe: Shallow pool in nature restauration area in Dwingelderveld near Spier, 52.8324° N, 6.4788° E, among submerged mosses on sandy soil, pH 7.3, EC 22 μS cm-1. Van Westen, 4 May 2015 (holotype L! Hugo de Vries Lab 2018.04, preserved as a fixed natural sample).

Differential diagnosis:— Cosmarium spierense belongs to the group of small crenate Cosmarium -species with a central ornamentation consisting of curved vertical rows of small granules. It could be compared with C. subcostatum Nordstedt (1876: 37 , pl. 12: 13) but semicells of that species are trapeziform in outline and have a less elaborate central ornamentation. Our algal form rather should be compared with Cosmarium norvegicum Strøm (1926: 214 , pl. 5: 15, 16). The latter is a but little known species and has been reported only a few times. In Europe, only by Strøm from Norway and by Förster (1967) from Sweden. Taylor (1934) reported this species from Newfoundland, Irénée-Marie (1939) from Canada and Fučíková et al (2008) from the USA. They invariably draw vertical rows of granules in the central ornamentation, nowhere the big, central wrath characteristic of our taxon is mentioned or depicted. Moreover, in C. norvegicum the outline of the semicells is semielliptic to semicircular (with the largest breadth at the base) rather than suboblong (with the largest breadth about halfway) as in our material. With respect to that latter feature, our taxon much resembles C. subcostatum var. spetsbergense Borge (1911: 18 , fig. 13). As, however, Borge does not describe or depict the central ornamentation of that variety, and we are of opinion that our taxon essentially differs from C. subcostatum , we prefer to render our alga the status of a separate species under a new name. The name of the species refers to the village where an abundant and sporulating population was found.

Ecology and geographical distribution: — C. spierense was encountered at several locations in Drenthe between mosses in slightly acidic to neutral, oligotrophic, shallow pools on sandy soil. Remarkably, this species was also found in a sample from Iceland (leg. D. Vuijk, 2016) in a more or less comparable environment. It cannot be excluded that C. spierense is an arctic-alpine element in the desmid flora of the Netherlands.

Figures

FIGURES 1–8. 1. Closterium joostenii. 2. Closterium cynthiaforme. 3. Staurastrum subcomptum. 4. Staurastrum exlooënse.5. Cosmarium abbreviatiforme. 6. Cosmarium kouwetsii. 7. Zygospore of Cosmarium spierense with adhering gametangial cells. 8. Cosmarium spierense.

FIGURES 27–40. 27, 29–38. Single cells of Cosmarium spierense (35–38. SEM microphotographs). 28. Zygospore of Cosmarium spierense. 39, 40. immature and mature zygospore of Cosmarium spierense with adhering gametangial cells. Scale bar = 10 μm.