Euastrum abruptum Nordstedt var. chapadae F.M.Costa, G.J.P.Ramos & C.W.N.Moura, 2018

Costa, Fabiana De Matos, Ramos, Geraldo José Peixoto, Oliveira, Ivaniabatista, Bicudo, Carlos Eduardo De Mattos & Moura, Carlos Wallace Do Nascimento, 2018, Five new taxa and a new record of Euastrum (Desmidiaceae) from the Chapada Diamantina region, Bahia State, Brazil, Phytotaxa 372 (3), pp. 193-202 : 195-196

Euastrum abruptum Nordstedt var. chapadae F.M.Costa, G.J.P.Ramos & C.W.N.Moura , var. nov. ( Figs. 2–5 )

Cells in frontal view subrectangular, apical lobes ornamented with 1 large spine, deep V-shaped incision. Basal lobes with spines small at the angles. Semicells decorated with 1 central protrusion, diagonally placed, 2 circular scrobicles and 1 pair of granules above. 1 scrobicle on the lateral side of the base of the apical lobe, granules in the median region of the apical lobe. Semicells in lateral view ovoid, in apical view rectangular. Cell wall slightly punctate. Zygospores not observed. Dimensions: Cells 27–31 μm long, 17–19.4 μm wide, polar lobe 11.3–14 μm wide, isthmus 5–7 μm wide.

Holotype (here designated): material numbered ( HUEFS 241800 !) deposited at Herbário da Universidade Estadual de Feira de Santana , population partially illustrated here in LM ( Figs. 2–4 ) and SEM ( Fig. 5 ) . Paratypes: HUEFS 241801, HUEFS 241802, HUEFS 241803.

Type material: BRAZIL. Bahia: Andaraí, Collected at “Marimbus do Baiano”, Pantanal dos Marimbus (Baiano Lagoon), 12° 45’ 54S, 41° 18’ 41.3”W. Sample collected by F. M. Costa, G. J. P. Ramos & C. W. N. Moura.

Habitat: Periphyton; conductivity 0.10 (± 0.02 mS. cm-1); dissolved oxygen 7.3 (± 1.7 mg.L- 1); pH 7.3 (± 0.2); total dissolved solids0.04 (± 0.01 ppt); water temperature 25.5 (± 2.1 ºC); water transparency 0.76 (± 0.13 m).

Etymology: —The specific epithet refers to the Chapada Diamantina, central Bahia State, Brazil, where the taxon occurs.

Differential diagnosis: — Euastrum abruptum var. chapadae differs from the other varieties of E. abruptum by having semicells with diagonally opposed central protrusions, deep V-shaped apical incisions, apical lobes with submarginal scrobiculae on the lateral sides of the base, and slightly concave margins.

Euastrum abruptum var. chapadae is morphologically similar to E. abruptum var. subglaziovii Krieger (1937: 606) and E. abruptum var. subglaziovii f. inflatum Prescott in Prescott et al (1977: 12); var. subglaziovii is distinct by having larger cells, upper margins truncate, apical incision shallow and closed, and the semicell surface has protrusions composed of three granules ( Krieger 1937; Prescott et al. 1977); var. subglaziovii f. inflatum differs by having the angles of its basal lobes rounded and prominent, a deep incision, and upper margins slightly concave ( Prescott et al. 1977).

We observed some specimens of E. abruptum var. chapadae among the populations analyzed having slightly closed apical incisions, and others having spines with larger apical angles.

The use of SEM was invaluable for observing a number of characteristics not discernible using light microscopy (LM)—such as the presence of scrobiculae at the base of the apical lobe and the presence of granules near the opening of the apical incision.

Figures

FIGURES 2–14. Euastrum abruptum var. chapadae var. nov.: LM (2–4); SEM (5), frontal view (2, 3, 5), lateral view (4). Euastrum fissum var. nordestinum var. nov.: LM (6–8); SEM (9). Euastrum groenbladii: LM (10–13); SEM (14), head of arrows indicating a line composed of supra-isthmal granules; frontal view (10, 11, 14), apical view (12), lateral view (13). Scale Bars: 10 μm.