Cosmarium trinodulum Nordstedt (1880:5)

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 : 295-297

Cosmarium trinodulum Nordstedt (1880:5) ( Figs 6 , 39–45 )

Cell dimensions: length 37–38 μm, breadth 34–35 μm, breadth of isthmus 6–7 μm

Material examined:— BRAZIL. Pantanal dos Marimbus,Andaraí, Bahia State. Sample: HUEFS 242434, HUEFS 241798.

Habitat:—This species was found associated with periphyton of Utricularia foliosa and Cabomba caroliniana . EC 0.04 (± 0.03 mS cm-1), DO 7.3 (± 1.2 mg L- 1), pH 7.6 (± 0.9), TDS 0.02 (± 0.01), T 27.9 (± 1.1 ºC), WT 0.82 (± 0.16 m)

Note:— Cosmarium trinodulum is a rare species, described by Nordstedt based on specimens associated with Utricularia collected in Caracas, Venezuela. This species is characterized by having generally subsemicircular semicells, apices rounded to truncate, with 5 vertical series of granules interconnected in the face of the semicells. The nominate variety is known in Brazil and Venezuela. There are also four varieties differing mainly in the pattern of granules on the face of the semicell: var. insigne Grönblad , var. glabrum Borge , var. pilgeri Schmidle , var. brasiliense Borge. With exception of var. insigne , which occurs in Finland, all other three varieties were described based on material from South America, the latter two from Brazil.

In the material from the Marimbus, we noticed a wide variation in the shape of the semicells and in the granules arrangement. The semicell ranged from subsemicircular, subtrapeziform to subrectangular, apices rounded to truncate, and lateral margins rounded to slightly crenate ( Fig. 6 ). The morphotype most common in the study area ( Figs. 39–41, 45 ) is similar to Cosmarium trinodulum forma reported by Borge (1903, pg. 92, Pl. 3, fig. 1) from specimens collected at Cachoeira ( RS), southern Brazil. Those specimens have granules with similar arrangement (spatially arranged over most part of the semicell, not just restricted to the median region as originally illustrated in the nominate variety by Nordstedt, tab. 1, Fig. 4 ), differing from those of the Marimbus in having no ridges connecting them. Sometimes these ridges are not well visible in LM, so it is possible Borge did not see them in those specimens from Cachoeira. The number and arrangement of granules is quite variable, but generally they are numerous and spatially arranged. It is possible to find a semicell with many granules, whereas the other one has but some of them, although usually located next to apical margins.

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).