Hypoxylon thailandicum Rathnayaka, K. D. Hyde & Chethana, 2025

Rathnayaka, Achala R., Chethana, K. W. Thilini, Manowong, Areerat, Bhagya, Amuhenage T., Win, Hsan, Tun, Zaw L., Mapook, Ausana & Hyde, Kevin D., 2025, Taxonomy, phylogeny, and bioactive potential of Xylariales (Sordariomycetes, Ascomycota) from Thailand: novel species discovery, new host and geographical records, and antibacterial properties, MycoKeys 120, pp. 35-117 : 35-117

Hypoxylon thailandicum Rathnayaka, K. D. Hyde & Chethana sp. nov.

Fig. 14

Etymology.

The epithet thailandicum refers to Thailand, where the fungus was collected.

Holotype.

MFLU 24-0530 .

Description.

Saprobic on a dead branch of Bambusa vulgaris . Sexual morph: Stromata 0.3–1 cm long × 0.1–0.5 cm wide, pulvinate, with conspicuous perithecial mounds, gregarious, surface bright orange; orange-red granules immediately beneath the surface and between ascomata, the tissue below the perithecial layer inconspicuous. Ascomata 200–220 × 195–203 × 180–210 µm (x ̄ = 210 × 200 × 190 µm, n = 5), globose, ostiolate. Peridium 21–27 μm wide, two-layered, outer layer composed of dark brown to brown cells of textura angularis, inner layer composed of hyaline cells of textura angularis. Asci 60–105 × 8–11 µm (x ̄ = 80 × 9.4 µm, n = 15), 8 - spored, unitunicate, cylindrical, pedicellate, with an inamyloid, apical ascal apparatus. Ascospores 13–18 × 7–10 µm (x ̄ = 16 × 8.4 µm, n = 30), uniseriate, slightly overlapping, one-celled, ellipsoid, with narrowly rounded ends, straight, initially light brown, becoming brown to dark brown at maturity, rough surface, guttulate. Asexual morph: Undetermined.

Culture characters.

Ascospores germinated on the PDA within 24 hours at 25 ° C. Germ tubes are produced from both sides of the ascospore. The slow-growing colonies on the PDA reach 1–2 cm diam. after seven days at 25 ° C, circular in shape, cottony, slightly less dense towards the edge, white color in the front view, and pale yellow in the reverse view.

Material examined.

Thailand • Chiang Rai, Mae Chan District, Mae Chan village , on a dead branch of Bambusa vulgaris ( Poaceae ), 18 March 2024, Achala Rathnayaka, AA 06 ( MFLU 24-0530 , holotype); ex-type living culture, MFLUCC 25-0024 .

Notes.

In multi-gene phylogeny (ITS, LSU, rpb 2, and β-tub), our novel isolates ( MFLU 24-0530 and MFLUCC 25-0024 ) formed a separate lineage sister to H. begae (S 99 and YMJ 215 ) and H. blackburniae ( BRIP 72467 b) with 97 % ML bootstrap and 0.95 PP support (Fig. 13 ). Morphologically, our new fungal collection ( MFLUCC 25-0024 ) is similar to Hypoxylon by having ascomata embedded in colorful effused or pulvinate stromata ( Ju and Rogers 1996). Due to the lack of morphological data for H. begae and H. blackburniae , we could not compare the morphological characters between these three species. When comparing the ITS base pair differences (without gaps) between H. thailandicum ( MFLUCC 25-0024 ) with H. begae ( YMJ 215 ) and H. blackburniae ( BRIP 72467 b), there are 9.5 % (46 / 482) and 9.12 % (44 / 482) differences, respectively. For β-tub, there is a 10.21 % (43 / 423) base pair difference (without gaps) between H. thailandicum ( MFLUCC 25-0024 ) and H. begae ( YMJ 215 ). However, due to the lack of sequence availability, we were unable to compare the base pair differences between H. thailandicum ( MFLUCC 25-0024 ) and H. blackburniae ( BRIP 72467 b). Additionally, the absence of rpb 2 sequences prevented a comparison among H. begae , H. blackburniae , and our collection. Based on the available morphological and phylogenetic evidence, we propose H. thailandicum as a new species.

Figures

Figure 13. Phylogram generated from ML analysis based on the combined dataset of ITS, LSU, rpb 2, and β-tub. The tree is rooted to Graphostroma platystomum (CBS 270.87), Natonodosa speciosa (CLM RV 86), Xylaria arbuscula (CBS 126415), and X. hypoxylon (CBS 122620). Bootstrap support values for ML ≥ 70 % and Bayesian posterior probabilities (PP) ≥ 0.90 are noted at the nodes. Strain numbers are noted after the species names. Strains isolated in this study are represented in blue, and type strains are in bold.

Figure 14. Hypoxylon thailandicum on a dead branch of Bambusa vulgaris (MFLU 24-0530, Holotype). a. Substrate; b – d. Appearance of ascostromata on the host; e, f. A horizontal section through an ascoma; g. Peridium; h – j. Asci; k. Inamyloid apical ascal apparatus stained with Melzer’s reagent; l – o. Ascospores; p. A germinated ascospore; q, r. Colony on the PDA (q upper, r lower). Scale bars: 1 mm (b); 200 μm (c, d); 100 μm (e, f); 20 μm (h – k); 10 μm (g, l – p).