Euastrum piataense G.J.P.Ramos & C.W.N.Moura, 2019

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 : 190

Euastrum piataense G.J.P.Ramos & C.W.N.Moura , sp. nov. ( Figs 28–34 )

Cells somewhat longer than wide; semicells pyramidal with concave sides; median constriction deep with sinus closed; apical incision open, U-shaped; basal and apical lobes ornamented with spines, apical angles with 1–2 spines; cell wall finely scrobiculate, with 2 spines near the margins of the basal lobes, a pronounced central protuberance, circular; 2 converging scrobicles in the mid-region; chloroplast with two pyrenoids. Zygospore not observed. Cell dimensions: length 70–80 μm, breadth 50–60 μm, apical lobe 30–36 μm, isthmus 14–16 um.

Holotype: material numbered ( HUEFS 244149 !) deposited at Herbário da Universidade Estadual de Feira de Santana , population partially illustrated here in LM ( Figs 28–32 ) and SEM ( Fig. 33–34 )

Etymology: The epithet refers to Piatã, type locality.

Type locality and habitat characteristics: Collected at “Barragem do Dragão” Piatã , Bahia state, Brazil. Lat. 13° 05’ 48” S, Long. 41° 51’ 02” W. Sample collected by G. J. P. Ramos , C. W. N. Moura, F. M. Costa and M. A. Santos s/n ( HUEFS 244149 ) on 13 July 2017. Euastrum piataense occurred in periphyton ; water temperature 21ºC, pH 7.8, conductivity 10 μS. cm-1, dissolved oxygen 9.2 mg.L- 1.

Notes: At first glance, this new species closely resembles Euastrum evolutum (Nordstedt) West & G.S. West (1896: 243) and its forms. The latter species differs, however, by having a polar lobe with a deep, V-shaped incision, as well as semicells with deep interlobar incisions and three granules arranged in a circle in the mid-region. E. evolutum also has cell walls smooth, whereas the new species has cell walls finely scrobiculate.

Another similar species is E. bidentatum var. peruvianum Willi Krieg. & A.M.Scott (1957: 132) , which differs from E. piataense by not having two central scrobicles in the mid-region, and by having an apical V-shaped incision and a number of granules near the lateral margins. Euastrum piataense occurred in large numbers in the sample we examined.

Figures

FIGURES 28–50. Euastrum piataense (28–34): LM (28–31), SEM (33,34), ventral view (28–30, 33), lateral view (31,34) apical view (32); Euastrum subcyclopicum var. elongatum (35–39): LM (35–38), SEM (39), ventral view (35–36, 39), lateral view (37), apical view (38); Euastrum bicudoi (40–42): ventral view (40), lateral view (41), apical view (42); Euastrum subtrilobulatum var. laeve (Figs 43–46): ventral view (43,44), lateral view (45), apical view (46); Micrasterias arcuata var. perforata (47–50): LM (47–49), SEM (50), zygospore (49). Scale bar 10 μm.