Amphibambusa aquatica Doilom sp. nov.

Index Fungorum number: IF 901394; Mycobank number: MB 901394; Facesoffungi number: FoF 16063; Fig. 1

Etymology – In reference to the freshwater habitat

Holotype – MFLU 18-1172

Saprobic on decaying wood submerged in freshwater. Sexual morph: Ascomata 400–900 μm high, 500–1000 μm diam., black, scattered, immersed, subglobose, unilocular, thin-walled, ostiolate, ostiolar opening with a mass of spores accumulated on the surface of substratum, forming a black, glistening, subglobose group of spores. Peridium 15–45 μm thick, comprising several layers of dark brown to black, thin-walled cells of textura angularis. Paraphyses even in width, 2–4 μm diam., numerous, cylindrical, branched, hyaline, aseptate. Asci 190–240×12–16 μm (x̅=215×15 μm, n = 10), 8-spored, unitunicate, cylindrical, thin-walled, pedicellate, apically rounded with a cylindrical, refractive, subapical ring, 1–2 μm high, 2–3 μm diam. Ascospores 32–40×6–7.5 μm (x̅=35×6.5 μm, n=20), mostly uni-seriate or overlapping uni-seriate, occasionally biseriate in the middle part, straight or slightly curved, hyaline, 1–2(-3)-septate, fusiform, pointed at both ends, thin-walled, smooth, guttulate, with a longitudinally striated wall and surrounded by 2–4(-7) μm thick, gelatinous sheath. Asexual morph: Not observed.

Culture characteristics – On PDA, colony circular, reaching 50 mm in 25 days at 25 °C, white from above, pale brown from below, surface rough, dry, raised, edge entire.

Material examined – China, Dehong, Yunnan Province, on submerged wood in a small river, 25 November 2017, G.N. Wang, H12A-1 (MFLU 18-1172, holotype); ex-type MFLUCC 18-1046; ibid., H12A-2 (HKAS 101747, isotype); ex-isotype KUMCC 18-0099.

GenBank numbers – ITS: PP584660; LSU: PP584659.

Notes – Amphibambusa aquatica shares morphology with the type species of Amphibambusa (A. bambusicola) in having immersed ascomata with an opening ostiolar, cylindrical asci, subapical ring, fusiform ascospores with a longitudinally striated wall, and being surrounded by a wide gelatinous sheath. However, A. aquatica has immersed ascomata with the opening ostiolar covered by a black, glistening, subglobose group of spores, while A. bambusicola has immersed ascomata under a small blackened clypeus and is surrounded by a white margin. Paraphyses of A. aquatica are even in width with aseptate, while they are uneven in width with septate of A. bambusicola. Amphibambusa aquatica has longer and narrower asci than those of A. bambusicola (190–240 × 12–16 μm vs. 150–200×17.5–20 μm). The ascospores of A. aquatica are mostly uni-seriate, 1–2(-3)-septate being surrounded by 2–4(-7) μm thick sheath, while they are biseriate, 1-septate asco surrounded by 10 μm thick sheath A. bambusicola (Liu et al. 2015a, b). In addition, A. aquatica has different culture characteristics on PDA from A. bambusicola (entire at the margin vs. irregular at the margin). The phylogenetic analysis of combined LSU and ITS showed that A. aquatica clustered in a sister branch with A. bambusicola resided in the family Cainiaceae (Fig. 2). Based on the differences in morphological characteristics and phylogenetic analysis, we introduce A. aquatica, a freshwater taxon, as a new species in Amphibambusa.

Figure 1 – Amphibambusa aquatica (MFLU 18-1172, holotype). a, b Appearance of subglobose group of spores on host surface. c Immersed ascomata with opening ostiolar on host surface. d Cross section of ascoma showing perithecium. e Structure of peridium. f–h Unitunicate asci. i Paraphyses. j–n Ascospores. o Germinated ascospore. p Colony on PDA (from front). q Colony on PDA (from below). Scale bars: e–i=20 μm, j–n=10 μm, o=30 μm

Figure 2 – Phylogram generated from maximum likelihood analysis based on combined LSU and ITS sequence data. The tree is rooted with Barrmaelia macrospora (CBS 142768) and B. rhamnicola (CBS 142772). ML bootstrap values equal to or greater than 75% and posterior probabilities equal to or greater than 95% are given above the nodes (ML/BYPP). Ex-type strains are in bold, and the new isolate is indicated in blue