Euastrum marimbusense 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 : 197-199

Euastrum marimbusense F.M.Costa, G.J.P.Ramos & C.W.N.Moura , sp. nov. ( Figs. 15–19 )

Semicells in frontal view subtrapeziform, apical lobes short, with angles convex, median incision shallow, open. Lateral lobes broadly rounded, 1 spine at the angles of the opening of the sinus. Semicells decorated with 1 scrobicle deep and circular, 1 rounded granule just above. 1 flattened granule covering the isthmus. Semicells in lateral view subrectangular and apical view elliptic. Cell wall with spaced punctuations. Zygospores not observed. Dimensions: Cells 17–19 μm long, 10–11 μm wide, lobe polar 7–8 μm wide, isthmus 3–4 μm wide.

Holotype (here designated): material numbered ( HUEFS 241796 !) deposited at Herbário da Universidade Estadual de Feira de Santana , population partially illustrated here in LM ( Figs. 15–18 ) and SEM ( Fig. 19 ) . Paratypes: HUEFS 241797, HUEFS 241798, HUEFS 241799.

Type material: BRAZIL. Bahia: Andaraí, Collected at “Marimbus do Baiano”, Pantanal dos Marimbus (Baiano Lagoon), 12° 45’ 53.8”S, 41° 18’ 38.3”W. Sample collected by F. M. Costa, G. J. P. Ramos & C. W. N. Moura.

Habitat: Periphyton; conductivity 0.08 (± 0.01 mS. cm-1); dissolved oxygen 8.2 (± 2.3 mg.L- 1); pH 7.1 (± 0.5); total dissolved solids0.03 (± 0.01 ppt); water temperature 27.5 (± 0.6 ºC); water transparency 0.52 (± 0.20 m).

Etymology: —The epithet refers to the Marimbus wetlands (Pantanal dos Marimbus) where the species occurs.

Differential diagnosis: — Euastrum marimbusense differs from the other species of the genus by having a large, circular, central scrobiculae on its surface, and 1 prominent rounded granule just above it, cell margins totally lacking spines, apical incision shallow, and a prominent flattened granule covering the isthmus.

Morphologically, Euastrum marimbusense resembles E. dubium Nägeli (1849: 122) , although the latter differs by having larger cell dimensions, the margins of the basal lobes ornamented with spines, a deep apical incision, and principally, the surfaces of the semicells ornamented with various granules and scrobiculae, as can be seen in the illustrations provided by Nägeli (1849: pl.7d, fig.2) and Prescott et al. (1977: pl.74, fig. 3). Euastrum marimbusense also resembles E. biscrobiculatum (Woloszynska) Coesel (2007: 9) in terms of their cell outlines, although the latter differs in terms of its surface decorations, including a prominent tubercle above the isthmus, and 2(–3) scrobiculae and a small granule just above it ( Coesel 2007: fig.18).

Although only a few specimens of E. marimbusense were encountered in the Pantanal dos Marimbus (Baiano Lagoon), it was possible to notice variations in terms of their cell shapes (circular or rectangular) and apical incisions (shallow or deep).

The morphological characteristics visible using SEM confirmed the observations made using LM, with emphasis on the flattened granule covering the isthmus—an uncommon characteristic in the genus.

Figures

FIGURES 15–30. Euastrum marimbusense sp. nov.: LM (15–18); SEM (19), frontal view (15, 16, 19), apical view (17), lateral view (18). Euastrum ornatiscrobiculatum sp. nov.: LM (20–24); SEM (25), head of arrows indicating scrobiculae along the lateral margins of the lobes; frontal view (20–22, 25), apical view (23), lateral view (24). Euastrum praemorsum var. foersteri var. nov.: LM (26–29); SEM (30), frontal view (26, 27, 30), apical view (28), lateral view (29). Scale Bars: 10 μm.