Cosmarium kanetsunae G.J.P.Ramos & C.W.N.Moura

Ramos, Geraldo José Peixoto, Santos, Maria Aparecida Dos & Moura, Carlos Wallace Do Nascimento, 2021, Taxonomic notes on some Cosmarium species (Desmidiaceae, Zygnematophyceae) from Brazil, Phytotaxa 483 (3), pp. 291-299 : 294-295

Cosmarium kanetsunae G.J.P.Ramos & C.W.N.Moura , stat. et nom. nov. ( Figs 4 , 22–26 )

Synonym: Cosmarium laticollum var. minutum Kanetsuna Phycol. Res. 52: 163, figs. 10–12, 27–30. 2004.

Description: Cells 23–25 μm length, 23,5–26,5 μm breadth, 5,5–7,5 μm breadth of isthmus, 15–17,5 μm thickness, sub-circular, deeply constricted in the middle, the sinus is narrow and has an undulate margin but is slightly open at the extremity. Semicells in frontal view subsemicircular, with acutely rounded basal angles. Apices slightly flattened, noteworthy thickened. Semicells in lateral view obtriangular, in apical view inflated fusiform to rhomboid. Cell wall, when seen in frontal view, thickened with four small mucros on the lateral margins of the semicell. In lateral view, the number of mucros ranges from four (longitudinal arrangement) up to eight (triangular arrangement). In apical view, the number of mucros in each margin ranges from one up to three. Chloroplast axial, with a single pyrenoid in each semicell.

Type locality: Sete Quedas , Paraná, Argentina ( Kanetsuna 2004) .

Material examined:— BRAZIL. Pantanal dos Marimbus, Andaraí, Bahia State. Samples: HUEFS 242434, HUEFS 242429.

Habitat:—In Brazil this species was found associated with periphyton of Utricularia foliosa . EC 0.07 (± 0.03 mS cm-1), DO 6.6 (± 0.3 mg L- 1), pH 6.6 (± 0.6), TDS 0.03 (± 0.01), T 27.6 (± 0.2 ºC), WT 0.7 (± 0.14 m).

Note:—This species was originally proposed by Kanetsuna (2004) as a variety of C. laticollum Delponte (1878: 116 , pl. 8: 20–23) based on specimens gathered in Argentina. Although the cell outline (sub-circular) somewhat resembles that species, there are enough distinct features to separate that variety from C. laticollum and raise it to species level. The first one is the cell size, a feature that Kanetsuna considered the main reason to propose the variety, which is about half as large as that of the type and slightly broader than long. However, the morphological features which we consider most relevant are the apical and lateral views, as well as the cell wall pattern. Cosmarium laticollum differs from the C. kanetsunae in having apices broadly rounded, elliptical cells (not inflated) in apical view, rounded in lateral view, and cell wall is covered with numerous grains arranged in longitudinal series in frontal view and circular series in apical view, in addition to having only mucros in the basal angles.

Overall, Cosmarium kanetsunae is a rare taxon, apparently endemic to South America, known only from its type locality ( Argentina), and now, Brazil. There are some minor differences between the populations from those countries regarding the pattern of mucros in the lateral view. Whereas the Argentinian specimens have only a longitudinal series with four mucros, the Brazilian ones have up to eight mucros in a triangular arrangement. Moreover, the apical angles are most thickened. Despite that, we are not inclined to consider the two populations as distinct varieties, since that pattern can be a variable feature, and both populations occurred in similar habitats (swamps areas from South America). As the name minutum is already used in Cosmarium minutum Delponte (1878: 105) , we propose a new name in honour of the desmidologist Yoshiyasu Kanetsuna.

Figures

FIGURES 1–8. Line drawings. 1. Cosmarium boeckii var.areolatum 2. C. clepsydra var. incrassatum 3. C. heptangulare 4. C. kanetsunae 5. C. pygmaeum 6. C. trinodulum 7. C. trinodulum var. brasiliense 8. C. trinodulum var. pilgeri.

FIGURES 9–32. LM and SEM. 9–15. Cosmarium boeckii var. areolatum: LM (9–12), SEM (15), frontal view (9, 10, 15), lateral view (11, 12), apical view (13, 14), 16–21. C. clepsydra var. incrassatum: frontal view (16–19), lateral view (20), apical view (21), 22–26. C. heptangulare: LM (22–25), SEM (26), frontal view (22–23, 26), lateral view (24), apical view (25), 27–32. C. kanetsunae: frontal view (27–28), lateral view (29, 30), apical view (31, 32). Scale bar: 10 μm, except Fig. 15 (5 μm).