Euastrum foersteri A.M.Scott & Croasdale ex C.B.Araújo & C.E.M.Bicudo, 2023

Araújo, Camila Barbosa de, 2023, Taxonomic and nomenclatural notes on two desmid species from Brazil (Desmidiaceae, Zygnematophyceae), Notulae Algarum 269, pp. 1-4 : 1-2

Euastrum foersteri A.M.Scott & Croasdale ex C.B.Araújo & C.E.M.Bicudo , sp. nov.

Replaced designation: “ Euastrum Foersteri A,M.Scott & Croasdale ” in Scott, Grönblad & Croasdale Acta Botanica Fennica , 69: 32, figs 69, 70, 1965, nom. inval.

Description: Cell as long as wide; semicell subquadrangular, 4-lobed, apical margin with deep median incision, rounded apical angles, one long, pointed spine; lateral margins concave, subquadrangular, basal angles with short, divergent, bifurcate spines; each semicell with a large truncate central papilla; median constriction deep, median sinus open, acute-angled; cell wall smooth; chloroplast axial. Cells 25-30 μm long (with spines), 19-21 μm (without spines), 20-26 μm wide (with spines), 16.5-21 μm (without spines), 4-4.5 μm isthmus width, 13-14 μm wide at apex (without spines).

Holotype: Förster (1964: pl. 6: fig. 5 [top specimen, two views of the same specimen], as “ Euastrum arciferum var. longispinum Förster ”; ICN Art. 40.5, Turland & al. 2018), here reproduced as Fig. 1 .

Type locality: Rio da Femmeas, state of Tocantins, Brazil.

PhycoBank Registration: 103604

Etymology: Named in honour of the eminent desmidologist Kurt Förster (1918–1983), who originally described the material.

Occurrence in Brazil: Rio da Femmeas, Tocantins state ( Förster 1964, Goiás state; as “ Euastrum arciferum var. longispinum Kurt Förster ”, nom. inval.); Arapiuns river – Lake Curi and Lake Mentaí ( Scott & al. 1965, as “ Euastrum foersteri Scott & Croasdale ”, nom. inval.), Lake Jurucuí ( Förster 1969, “ Euastrum foersteri Scott & Croasdale ”, nom. inval.), Pará state; Nhamundá Region, Amazonas state ( Thomasson 1977, just citation).

The name “ Pleurotaenium tridentulum var. tenuissimum ” introduced by Grönblad & Croasdale (in Scott & al. 1965: 30, pl. 2: figs 33-34) and a new combination “ Pleurotaenium tenuissimum Förster ” ( Förster 1981: 246) were not validly published since they were also not based on a single gathering (ICN Art. 40.2, Shenzhen Code, Turland & al. 2018), and a type locality was not designated from the two localities listed in Scott & al. (1965): “Rio Arapiuns”, above the “Ponta Icuxi” (Nr. 20, a tributary of the Tapajós River, Pará state, Brazil) and the mouth of “Rio Uaupés” (Nr. 21, a tributary of the Rio Negro basin, state of Amazonas, Brazil). Although Grönblad & Croasdale (1971: 40) designated fig. 34 of Scott & al. (1965) as the holotype, the designation “ Pleurotaenium tridentulum var. tenuissimum ” remains invalid as a full and direct reference the place of valid publication, with page or plate reference and date were not given (ICN Art. 41.5, Shenzhen Code, Turland & al. 2018). Furthermore, the shape of “ Pleurotaenium tridentulum var. tenuissimum ” deviates considerably from the shape of P. tridentulum species ( Förster 1981). Furthemore, Pleurotaenium tridentulum (Wolle) West is now considered a heterotypic later synonym of Pleurotaenium sceptrum (Roy) West & G.S.West (e.g. Prescott & al. 1975; Araújo & al. 2022). Thus, we here validate “ Pleurotaenium tenuissimum ” by providing it with a formal description and a type based on the material studied by Grönblad & Croasdale (in Scott & al. 1965) and Kurt Förster (in Förster 1969, 1974, 1981). Also, we link here all taxa and their published illustrations that represents this species and its distribution in Brazil.

Figures

Figs. 1-6. Nomenclatural types of desmid names proposed herein. Fig. 1. Holotype (top two views) of Euastrum foersteri sp. nov.: original illustration of “Euastrum arciferum var. longispinum Kurt Förster & Eckert” (in Förster 1964: p. 349, pl. 6: fig. 5). Fig. 2. Euastrum foersteri sp. nov.: