Cosmarium dimaziforme var. concavum Kurt Först. & F.Eckert ex Kurt Först. (1981: 228)

Ramos, Geraldo José Peixoto, Costa, Fabiana De Matos, Santos, Maria Aparecida Dos & Moura, Carlos Wallace Do Nascimento, 2019, Taxonomic novelties, new records, and rare species of desmids from the Chapada Diamantina region, Brazil, Phytotaxa 391 (3), pp. 185-196 : 187

Cosmarium dimaziforme var. concavum Kurt Först. & F.Eckert ex Kurt Först. (1981: 228) ( Figs 7–10 )

Cell dimensions: length 16–18 μm, breadth 20–22 μm, isthmus 6–8 μm.

Habitat characteristics: River; water temperature 19ºC, pH 7.2, conductivity 20 μS. cm-1, dissolved oxygen 7.3 mg.L- 1.

Material examined: HUEFS 244150.

Notes: This variety was described by Förster (1964) from material collected in Serra da Lua , northern Brazil. It differs from the nominate variety mainly by having cells 1.2 times wider than long, a concave apex, apical angles, and lateral lobes with a wart and smooth membrane. The taxon resembles Cosmarium pileatum var. brasiliense (Grönblad) Willi Krieg. & Gerloff (1969:318) , which differs mainly by having acute-angled open sinus, truncate apices, and the central region of the semicell has only a prominent inflation, while C. dimaziforme var. concavum has three verrucae (best seen in apical view).

Cosmarium dimaziforme var. concavum was reported for coastal lagoons along the north littoral region (Conde, Esplanada, Entre Rios) of Bahia by Oliveira et al. (2016). In the illustration provided by those authors ( Fig. 19 ), however, the identification of this taxon was apparently misapplied, because it does not show the concave margins characteristic of this variety, but rather shows apical margins truncated, approaching those of Cosmarium dimaziforme var. goyazense Kurt Först. & F.Eckert (1964: 389) . Thus, the taxon under discussion from the Chapada Diamantina is the first confirmed record of C. dimaziforme var. concavum for northeastern Brazil.

Figures

FIGURES 2–27. Cosmarium diamantinum (2–6): ventral view (2–4), lateral view (5) apical view (6); Cosmarium dimaziforme var. concavum (7–10): ventral view (7), lateral view (8) apical view (9), cell division (10); Cosmarium pentachondrum (11–13): ventral view (11), lateral view (12) apical view (13); Euastrum bahiense (14–16): ventral view (14), lateral view (15) apical view (16); Euastrum croasdaleae var. incrassatum (17–20): ventral view (17,18), lateral view (19) apical view (20); Euastrum duplicato-verrucosum (21–25): ventral view (21,22), lateral view (23) apical view (24), zygospore (25); Euastrum octogibbosum (26–27): LM (26), SEM (27). Scale bar 10 μm.