Cosmarium pygmaeum W.Archer

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 : 295

Cosmarium pygmaeum W.Archer ( Fig. 5 , 33–38 )

Cell dimensions: length 7–8 μm, breadth 8,5–9 μm, breadth of isthmus 3–3,5 μm.

Material examined:— BRAZIL. Pantanal dos Marimbus, Andaraí, Bahia State. Samples: HUEFS 253745, HUEFS 253766

Habitat:—This species was found associated with periphyton of Utricularia foliosa and Cabomba caroliniana . EC 0.02 (± 0.01 mS cm-1), DO 6.3 (± 0.3 mg L- 1), pH 7.5 (± 0.8), TDS 0.01 (± 0.005), T 29.8 (± 1.8 ºC), WT 0.6 (± 0.18m)

Note:— Cosmarium pygmaeum is a species with cosmopolitan distribution, with a bunch of records mainly in Europe ( Guiry & Guiry 2020). However, in Brazil and even in South America, this species is rarely reported in the literature. There is only a record of its occurrence in the Brazilian territory, which was based on the sample gathered in municipality of Rio Claro, State of São Paulo (Bicudo 1969, Bicudo et al. 2019). Thus, the material from Bahia represents the second record of that species in Brazil. Overall, it is one of the most polymorphic and smaller Cosmarium taxa occurring in the Marimbus. The main morphological variations in the specimens from Bahia are the sinus, from open to closed, the central granule which can be next to the apical margin or close to the isthmus, and the papillae at the basal angles, which could be more or less projected ( Fig. 5 ). According to Kouwets (1987) the arrangement of granules on the cell wall is very variable, and without any taxonomic value.

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 33–59. LM and SEM. 33–38. Cosmarium pygmaeum: LM (33–37), SEM (38), frontal view (33–35), lateral view (36), apical view (37), 39–45. C. trinodulum: LM (39–44), SEM (45): frontal view (39–42, 45), lateral view (43), apical view (44), 46–54. C. trinodulum var. brasiliense: LM (46–53), SEM (54), frontal view (46–50, 54), lateral view (51), apical view (52, 53), 55–59. C. trinodulum var. pilgeri: frontal view (55–57, 57—Cell division), lateral view (58), apical view (59). Scale bar: 10 μm, except Fig. 38 (2 μm).