Petriella thailandica O. Karimi & K.D. Hyde, sp. nov.

Index Fungorum number: IF 900454; MycoBank number: MB 900454; Facesoffungi number: FoF 13983; Fig. 1

Etymology – The name refers to Thailand, where the fungus was collected.

Saprobic on submerged wood in freshwater habitat. Sexual morph: Undetermined. Asexual morph: Conidiophores 785–1,350×25–115 µm (x=953×69 μm, n=50), synnematous, erect, flexuous, olivaceous brown to dark brown, consisting individual conidiophores (50–90 μm), septate. Synnemata abundant, 785–1,350×25–115 µm. Conidiogenous cells 10–45×1–2.7 µm (x=35×1.9 μm, n=50), cylindrical to sub cylindrical, long, branched profusely at the apex. Conidia 1.7–7.4 × 1–2.7 μm (x=4.4 × 1.7 μm, n=100), aseptate, hyaline, smooth, variable, ellipsoidal, reniform, obovoid, cylindrical.

Culture characteristics – Colonies on PDA reaching 40 mm diam. after 14 days at 25 °C, circular, flat, smooth margin, initially white, turning to creamy; reverse white. Mucoid conidial mass observed after five weeks.

Material examined – Thailand, Chiang Rai, Phan District, Doi Pui Sai Khao, on decaying submerged wood, 27 September 2021, O. Karimi, STS5B40 (MFLU 23-0001, holotype), ex-type culture MFLUCC 23-0001.

GenBank numbers – ITS: OQ172252; LSU: OQ172248; rpb2: OQ200123; β-tubulin: OQ184744.

Notes – Our petriella-like collection is morphologically similar to P. lindforsii Curzi and P. guttulata G.L. Barron & Cain. However, our collection differs from P. lindforsii in having long conidiophores (786–1,350 ×250–350 μm), and aseptate, ellipsoidal, reniform, obovoid to cylindrical, small conidia (1.7–7.4 × 1–2.7 μm) while P. lindforsii has mostly hyaline, cylindrical-oblong, large conidia (8–14 × 3.5–6 μm) with a papillate appendage at the proximal end (Barron et al. 1961). Our collection differs from P. guttulata in longer and wider synnemata (785–1350×25–115 µm vs 1000×6–25 µm) (Barron et al. 1961). In the combined ITS and LSU sequence analysis (Fig. 2) shows that our petriella-like collection forms a distinct clade and distant from P. lindforsii and P. guttulata. Therefore, we introduce this collection as Petriella thailandica.

Figure 1 – Petriella thailandica (MFLU 23-0001, holotype). a Host substrate. b Synnemata on substrate. c, d Synnemata. e, f Conidiogenous cells. g Conidia. h Surface view of colony on PDA. Scale bars: b=1 mm, c–f=70 μm, f=20 μm, g=7 μm

Figure 2 – The best scoring RAxML tree generated using ITS and LSU combined dataset with a final likelihood value of – 4609.603487 is presented The tree is rooted with Ramophialophora globispora (LC5789) and R. petraea (LC5696). The ML bootstrap values>60% and Bayesian posterior probabilities (PP)>0.9 are noted at the nodes. The new species is in blue bold. Twenty taxa are included in the combined analyses which comprise a total of 1346 characters. The matrix had 345 distinct alignment patterns, with 25.06% undetermined characters or gaps. Estimated base frequencies were as follows: A=0.252378, C=0.240783, G=0.285095, T=0.221744; substitution rates AC=1.743022, AG=2.583205, AT=1.866015, CG=1.345319, CT=7.144677, GT=1.0; gamma distribution shape parameter α=0.226347