Minutisphaera thailandensis R.J. Xu, Boonmee & K.D. Hyde, sp. nov.

Index Fungorum number: IF 558547; MycoBank number: MB 558547; Facesoffungi number: FoF 09943; Fig. 1

Etymology – The specific epithet “thailandensis” referring to the country from which the species was collected.

Holotype – MFLU 21-0094

Saprobic on submerged wood, submerged in freshwater habitats. Sexual morph Ascomata 80–108 µm high, 95–101 µm diam., immersed to erumpent, solitary, scattered, globose to subglobose, dark brown to black, ostiolate. Peridium thin, soft, composed of brown to dark brown cells of textura angularis. Hamathecium pseudoparaphyses not seen. Asci 40–56×15–27 µm (x̅=47×21 µm, n=10), 8-spored, bitunicate, obpyriform to broadly clavate, slightly curved, rounded at the apex, sessile to obtuse at the base. Ascospores 21–27×5–8 µm (x̅=24×7 µm, n=20), 2–3-seriate overlapping, ovoid to obovoid, apex wider, narrower towards the lower and rounded end, 1-septate, slightly above the middle, constricted at the septum, hyaline, surrounded by prominent mucilaginous sheath, sheath constricted the septum, with long filamentous appendages separating out of the sheath, numerous granular contents, smooth-walled. Asexual morph Undetermined.

Culture characteristics – Ascospores germinating on MEA within 12 h. Colonies on MEA, reaching 5 cm diam. after 4 weeks at room temperature, mycelium dense, brown to dark brown on surface, dark brown to black in reverse with entire edge.

Material examined – THAILAND, Chiang Rai Province, Mueang, Ban Nang Lae (99°52′52.93″ E 20°3′2.52″ N), on submerged wood in freshwater stream, 27 May 2020, R.J. Xu, MD-39 (MFLU 21-0094, holotype), ex-type living culture, MFLUCC 21-0072.

GenBank numbers – ITS=MZ493355, LSU=MZ493343, SSU=MZ493342.

Notes – Multigene phylogenetic analysis indicates our new taxon consistently clustered with Minutisphaera aquaticum with 100% MLBS, 1.00 BYPP support (Fig. 2). However, M. thailandensis (MFLUCC 21-0072) significantly differs from M. aquaticum in term of the ascospore features including having a septum located in the upper cell and possessing long filament appendages (Fig. 1). In addition, M. thailandensis shares similarly characterized ascomata and ascospores with some species, namely M. fimbriatispora and M. parafimbriatispora but they differ in shape and size (Ferrer et al. 2011; Raja et al. 2015). Furthermore, M. thailandensis differs from M. aspera and M. japonica in both shape and pigmentation of the ascospores (Raja et al. 2013, 2015). Therefore, Minutisphaera thailandensis is introduced as a new species based on its distinct morphology and phylogenetic evidence.

Figure 1 –  Minutisphaera thailandensis (MFLU 21-0094, holotype). a, b Ascomata on submerged wood. c, d Squash of ascoma. e–h Asci. i–n Ascospores. o Culture on PDA. Scale bars: c, d=50 μm, e–h=20 μm, i–n=10 μm

Figure 2 –  Phylogram generated from maximum likelihood analysis based on combined LSU, SSU and ITS sequence data representing the species of Minutisphaera in Minutisphaeraceae. Myrmaeciumrubricosum CBS139067 and M. rubrum CBS109505 are selected as the outgroup taxa. The best RAxML tree with a final likelihood value of − 17637.597976 is presented. RAxML analysis yielded 1292 distinct alignment patterns and 38.19% of undetermined characters or gaps. Estimated base frequencies were as follows: A=0.254974, C=0.223826, G=0.282377, T=0.238823, with substitution rates AC=1.255015, AG=2.734543, AT=1.149276, CG=1.117855, CT=6.544858, GT=1.000000; gamma distribution shape parameter alpha=0.206169. Bootstrap support values for maximum likelihood (MLBS, left) equal to or greater than 70% is given above the nodes. Bayesian posterior probabilities (BYPP, right) equal to or greater than 0.95 are given above the nodes. Ex-type strains are in bold and newly generated sequence is in blue