Cosmarium trinodulum var. brasiliense Borge (1899:20)

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 : 297

Cosmarium trinodulum var. brasiliense Borge (1899:20) ( Figs 7 , 46–54 )

Cell dimensions: length 35–39 μm, breadth 29–30 μm, breadth of isthmus 8–9 μm.

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

Habitat:—This variety was found associated with periphyton of Utricularia foliosa . EC 0.05 mS cm-1, DO 6.8 mg L- 1, pH 6.6, TDS 0.02, T 27.8 ºC, WT 0.6 m.

Note:— This variety differs from the nominate variety by having cells with 3 horizontal series of granules (5-5-3). The latter series next to isthmus has 3 granules, whereas the median and subapical ones have 5 granules. It is rather rare variety, only known till now from its type locality (Rio de Janeiro, Brazil) .

Unlike the type variety, the var. brasiliense rarely was found in the Marimbus. Still, we noticed a considerable morphological variation in the specimens of this variety from that area, mainly in the cell outline and in the number of granules. The basal margins ranged from rounded to crenate ( Fig. 7 ). The specimens with the first pattern generally have 1–2 arched series of granules, whereas the crenate ones have 2–3 series. Sometimes the series of 3 granules, next to the isthmus, is somewhat difficult to observe or even be lacking. We did not observe the connections between the granules in LM; however, some remnants are visible in SEM ( Fig. 54 ).

Gerrath (1979) studied the polymorphism in a population of Cosmarium taxichondrum Lundell (1871: 39) , another interesting species, remarkable by its set of granules. He noticed also a great variation in the granules arrangement, which some of them may even occasionally be lacking, such as our observations in C. trinodulum var. brasiliense . Apparently, the subapical series is the most consistent feature of this variety, at least it was observed in all specimens examined, whereas the series located next to isthmus is most variable.

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).