Closterium joostenii 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 : 3

Closterium joostenii Van Westen et Coesel sp. nov. ( Figs 1 , 12–14)

Cells rather strongly curved, gradually tapering from the middle to the poles. In general, towards the poles more strongly arched than in the middle. Apices narrowly rounded, no visible end pore. Cell wall colourless, without girdle bands, delicately striate (8–10 striae in 10 μm, in many cases hardly detectable).

Dimensions: length 110–160 μm, breadth 10–13 μm, L/B ratio 9.7–13.8, curvature 120 o –146 o.

Type:— THE NETHERLANDS. Drenthe: pool with Sphagnum in former quaking bog in estate Berkenrode, near Barger-Compascuum, 52.7632° N, 7.0073° E, in Sphagnum squeezing, pH 3,9 conductivity 38 μS cm-1. Van Westen, 15 June 2012 (holotype L! Hugo de Vries Lab 2018.01, preserved as a fixed natural sample).

Etymology:—The species is named after the Dutch phycologist Anton Joosten, who drew our attention to the characteristics of the above-described species.

Differential diagnosis and ecology:— Cl. joostenii can easily be confused with Cl. archerianum var. minus Skuja. Cl. archerianum var. minus , as originally described by Skuja (1949: 105, pl. 22: 16) from Burma, is an insufficiently known taxon that, compared to our species, has narrower and obliquely truncate apices, whereas the ventral side in the midregion is slightly inflated. That latter feature is wanting in Cl. archerianum var. minus as depicted in Růžička’s (1977, pl. 28: 7) flora. We cannot preclude that this picture refers to our newly described Cl. joostenii . Cl. joostenii is exclusively found in acidic, oligotrophic moorland pools with Sphagnum vegetation. In the province of Drenthe, this species was found in over 50 locations, mainly with pH between 3.5 and 6 and conductivity between 20 and 60 μS cm-1. If the fine cell wall striation is overlooked, this species can easily be confused with Cl. parvulum Nägeli , a species, however, with a completely different ecological preference.

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.