Pleurothecium aseptatum J. Ma & Y.Z. Lu, sp. nov.

Index Fungorum number: IF 900172; Mycobank number: MB 900172; Facesoffungi number: FoF 13907; Fig. 1

Etymology – referring to the aseptate conidia.

Holotype – GZAAS 22–2019.

Saprobic on submerged decaying wood. Sexual morph: undetermined. Asexual morph: Colonies on the substratum superficial, effuse, gregarious, white. Mycelium composed of partly immersed, partly superficial, hyaline, septate, branched hyphae, with a little of glistening conidia. Conidiophores macronematous, mononematous, erect, cylindrical, mostly unbranched, a few branched, 46–59 μm long (x = 53 μm, n=15), 1.5–2.5 μm wide (x = 2 μm, n=15), tapering to 0.8–1.3 μm wide near apex, 0–1-septate, sometimes reduced to conidiogenous cells, hyaline, smooth-walled. Conidiogenous cells polyblastic, integrated, terminal, sympodial, cylindrical, 41–53 μm, denticulate, hyaline; denticles cylindrical, long, narrow, 3–5×0.6–0.8 μm (x = 4×0.7 μm, n=20). Conidia solitary, acrogenous, subcylindrical, slightly curved, 8.5–10 μm × 2–3 μm (x = 9.5 × 2.5 μm, n=30), rounded at the apex, obtuse and tapering towards base, aseptate, with 2–4 large guttules, hyaline, smooth-walled.

Culture characteristics – Conidia germinating on water agar and germ tubes produced from conidia within 8 h. Colonies growing on PDA, circular, with flat surface, edge entire, reaching 45 mm in 30 days at 25 °C, pale brown to brown.

Material examined – China, Guizhou Province, Qiandongnan Miao and Dong Autonomous Prefecture, Tianzhu County, on decaying wood in a freshwater stream, 16 January 2021, Jian Ma, TZX8 (GZAAS 22–2019, holotype), ex-type living culture, GZCC 22–2019.

GenBank numbers – LSU=OQ002372, ITS=OQ002375.

Notes – Phylogenetically, Pleurothecium aseptatum is clustered within Pleurothecium and formed a basal clade to P. recurvatum and P. semifecundum (Fig. 2). Morphologically, P. aseptatum differs from P. recurvatum and P. Semifecundum by having hyaline conidiophores and aseptate conidia, while P. recurvatum and P. semifecundum having 3-septate conidia and brown conidiopheres (Réblová et al. 2012; Luo et al. 2019). Furthermore, the denticles of conidiogenous cells in P. aseptatum are rather long, while P. recurvatum and P. semifecundum having tiny denticles (Réblová et al. 2012; Luo et al. 2019).

Figure 1 – Pleurothecium aseptatum (GZAAS 22–2019, holotype). a, b Colonies on dead wood. c–i Conidiophores and conidiogenous cells. j, k, p Conidiogenous cells bearing conidia. l–o, s–u Conidia. v Germinated conidia. q, r Colony on PDA from above and below. Scale bars: c–k, p, v=10 μm, l–o, s–u=5 μm

Figure 2 – Phylogram generated from maximum likelihood analysis based on combined ITS, LSU, SSU and rpb2 sequence data representing the species of pleurotheciaceae. Thirty-nine taxa were included in the combined analyses, which comprised 3393 characters (ITS: 621, LSU: 870, SSU=986, rpb2=916) after alignment. Bootstrap support values for ML equal to or greater than 50% and BYPP equal to or greater than 0.95 are given above the nodes. Conioscypha minutispora (CBS 137253) and C. tenebrosa (GZCC 19-0217) were used as the outgroup taxa. The newly-generated strain is shown in blue and bold. Ex-type strains are indicated by black and bold