Pleurothecium takense Chuaseehar., Nuankaew, Somrith. & Boonyuen, sp. nov.

Index Fungorum number: IF 900198; Mycobank number: MB 900198; Facesoffungi number: FoF 15106; Fig. 1

Etymology – The specific epithet “takense” refers to the Tak Province, Thailand where the taxon was collected.

Holotype – BBH 49602

Saprobic on submerged twigs in freshwater habitat. Sexual morph: not observed. Asexual morph: Colonies on natural substratum effuse, hairy, brown to black with visible whitish to yellowish spore masses. Mycelium 2.5–5 μm diam, partly immersed, partly superficial, composed of branched, septate, smooth-walled, pale brown to brown hyphae. Conidiophores 213–550 × 3.3–4.8 μm (x̄=370 × 4.1 μm, n=20), macronematous, mononematous, solitary, simple, cylindrical, erect, straight or slightly flexuous, 6–11-septate, smooth-walled, brown to black below, paler towards the apex. Conidiogenous cells up to 35×3.7–7.5 μm, holoblastic, polyblastic, integrated, terminal, sometimes becoming intercalary, cylindrical, denticulate, sympodially elongating and recurved, pale brown to brown, with 3–13 or more cylindrical denticles, 1.3–2.8×1.2–2.3 μm. Conidiogenous locus occasionally formed an apical secondary conidiophore. Conidia 25–31×6.5–9 μm (x̄=27.7×7.7 μm, n=20), acropleurogenous, solitary, ellipsoidal, slightly curved, 3-septate, smooth-walled, central cells light brown to becoming brown at maturity, end cells paler. Conidial secession schizolytic.

Culture characteristics – Colonies on PDA reaching 18–21 mm diam., after 14 days at 25 °C, cottony with sulcate, grey, round, margins mostly entire, soluble pigment absent, exudates absent, reverse dark grey.

Material examined – Thailand, Tak Province, Mae Sot District, Pha Daeng Waterfall Nature Trail, on submerged twigs of an unidentified plant in a small freshwater stream, 24 May 2022, N. Boonyuen, isolate FF01100 (BBH 49602, holotype), ex-type, TBRC-BCC 95074; isolate FF01100.01 (BBH 49603, isotype), living culture, TBRCBCC 95075.

GenBank numbers – TBRC-BCC 95074: ITS=OQ121931, LSU = OQ121949, rpb2= OQ116754, SSU: OQ121940; TBRC-BCC 95075: ITS= OQ121932, LSU = OQ121950, rpb2=OQ116755, SSU: OQ121941, tef1-α=OQ116763.

Pleurothecium takense is phylogenetically related to P. floriforme, with 100% ML bootstrap and 1.00 BYPP supports (Fig. 2). Morphologically, the new taxon differs from P. floriforme in that it has pigmented conidia in maturity with light brown to brown central cells and paler end cells, whereas the latter has hyaline conidia (Hyde et al. 2017). Pleurothecium bicoloratum and P. recurvatum are most morphologically similar to P. takense, which has 3-septate, smooth-walled, pigmented conidia (Monteiro et al. 2016). Nevertheless, P. takense is different from P. recurvatum based on phylogenetic analysis (Fig. 2). Due to a lack of sequence data for P. bicoloratum, the phylogenetic position of P. bicoloratum could not be compared with our new species. Morphologically, P. bicoloratum differs in possessing strong pigment with dark olivaceous-brown to black at central cells and hyaline end cells and broadly allantoid conidia (Monteiro et al. 2016), whereas conidia in those two taxa (P. takense and P. recurvatum) are initially hyaline, later becoming pale brown to brown with central cells darker than end cells as they mature, with conidial shape varying from oblong to oblanceolate or somewhat falcate in P. recurvatum (Morgan 1895; Goos 1969), and ellipsoidal in P. takense (Fig. 1). Thus, one new species is described in this study as Pleurothecium takense.

Figure 1 – Mucispora maesotensis (BBH 49600, holotype). a, b Colonies on natural substrate. c–e Conidiophores with conidia. f Conidiophore. g–i Conidia. j–n Hyphae and conidiophores with conidia on PDA. o–r Conidia. Upper and reverse views of culture on PDA after 27 days at 25 °C. Scale bars: a, b=100 μm, c–r=20 μm

Figure 2 – Phylogram generated from maximum likelihood analysis (RAxML) of the Pleurotheciaceae based on the combined ITS, LSU and rpb2 sequence data. Seventy-four taxa are included in the combined analyses, which comprise 2,700 characters with gaps. Canalisporium caribense (SS 03839) and Savoryella lignicola (NTOU791) were chosen as the outgroup. The best scoring RAxML tree with a final likelihood value of − 27,078.871595 is presented. The matrix had 1,468 distinct alignment patterns, with 37.01% of undetermined characters or gaps. The proportion of invariable sites was 0.396394. Estimated base frequencies were as follows: A=0.215041, C=0.319662, G=0.285771, T=0.179525; substitution rates: AC=1.174315, AG=2.403151, AT=1.719399, CG=0.666160, CT=6.665075, GT=1.00000; gamma distribution shape parameter α=0.638780. Bootstrap support values for ML equal to or greater than 70% and BYPP equal to or greater than 0.95 are given near the nodes. T=ex-type strain. The newly generated sequences are indicated in blue bold