Rhexoacrodictys fangensis Chuaseehar., Nuankaew, Somrith. & Boonyuen, sp. nov.

Index Fungorum number: IF 900200; Mycobank number: MB 900200; Facesoffungi number: FoF 15107; Fig. 1

Etymology – The specific epithet “fangensis” refers to the Fang District, Chiang Mai Province, Thailand where is the type was collected.

Holotype – BBH 49598

Saprobic on submerged wood in freshwater habitat. Sexual morph: Not observed. Asexual morph: Colonies on natural substratum effuse, scattered, granulate, black. Mycelia 2–2.5 μm diam, mostly immersed, composed of branched, septate, smooth-walled, pale brown to brown hyphae. Conidiophores 12.5–37.5 × 3.7–5 μm (x̄=20×4.3 μm, n=20), macronematous, mononematous, solitary, simple, cylindrical, erect, straight, 1–5-septate, smooth-walled, brown, with 1 or more percurrent extensions at the upper part. Conidiogenous cells holoblastic, monoblastic, integrated, terminal, cylindrical, brown. Conidia 20–30 × 12.7–22.5 μm (x̄= 26.2 × 15.4 μm, n = 20), acrogenous, solitary, obovoid to obpyriform, oblong-ellipsoidal, muriform, with multiple longitudinal or oblique and transverse septa, smooth-walled, brown to dark brown and basal cell paler, apex rounded, basal cell protruding, cylindrical, with a distinct, 1–7 × 3.5–4 μm basal frill. Conidial secession rhezolytic.

Culture characteristics – Colonies after 14 days at 25 °C: On MEA attaining 13–14 mm diam, glabrous, white, round, margins entire, soluble pigment absent, exudates absent, reverse yellowish white with dark grey at center. On PDA reaching 16–25 mm diam, velvety with sulcate, olive grey with white margins, irregular, margins undulate, soluble pigment absent, exudates clear droplets, reverse medium grey with white margins.

Material examined – Thailand, Chiang Mai Province, Fang District, Khlong Pong Nam Dang, on submerged wood of an unidentified plant in a freshwater stream, 24 November 2021, N. Boonyuen and S. Nuankaew, isolate FF01084 (BBH 49598, holotype), ex-type, TBRC-BCC 94389; isolate FF01084.01 (BBH 49599, isotype), living culture, TBRC-BCC 94390.

GenBank numbers – TBRC-BCC 94389: ITS= OQ121933, LSU = OQ121951, rpb2= OQ116756, SSU: OQ121942, tef1-α=OQ116764; TBRC-BCC 94390: ITS= OQ121934, LSU = OQ121952, rpb2= OQ116757, SSU: OQ121943, tef1-α= OQ116765.

Notes – Rhexoacrodictys fangensis differs from the other accepted Rhexoacrodictys species (Species Fungorum; accessed 23 May 2024) by having the shortest conidiophores with one or more percurrent extensions at the apical part. In multi-gene phylogenetic analysis, based on the combined ITS, LSU, and rpb2 dataset (Fig. 2), the new species forms a sister relationship with R. fimicola. However, the support values for separation are low. Rhexoacrodictys fimicola is distinguished from R. fangensis by producing conidia which is evenly pigmented or without a dark brown basal cell and having longer conidiophores (up to 75 × 5–7 μm; Baker et al. 2002), while R. fangensis has unevenly pigmented conidia in brown to dark with basal cell paler and shorter conidiophores. Thus, our collection is different from known Rhexoacrodictys species, and it formed a distinct subclade in phylogenetic analyses. Based on the morphology and molecular data, we introduce our collection here as a new species.

Figure 1 – Rhexoacrodictys fangensis (BBH 49598, holotype). a, b Colonies on natural substrate. c–f Conidiophores and conidia. g conidiophore. h–k Conidia. l–o Upper and reverse views of culture on PDA (the top) and MEA (the bottom), after 14 days at 25 °C. Scale bars: a=100 μm, b=25 μm, c=20 μm, d–k=10 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