Stilbohypoxylon chiangraiense 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

Stilbohypoxylon chiangraiense Rathnayaka, K. D. Hyde & Chethana sp. nov.

Fig. 12

Etymology.

The epithet chiangraiense refers to Chiang Rai Province, where the fungus was collected.

Holotype.

MFLU 24-0529 .

Description.

Saprobic on a dead branch of Saraca sp. Sexual morph: Stromata superficial, visible as a black conical or globose structure on the host surface, solitary, showing yellow scales on mature stromata, carbonaceous, brittle, fragile. Ascomata 420–440 × 450–510 μm (x ̄ = 427 × 471 μm, n = 10), black, carbonaceous, globose to mammiform, 1 per stroma, covered with remnants of the host tissue, ostioles papillate. Peridium 10–20 μm wide, thick-walled, composed of several layers of cells of textura angularis, dark brown to black. Paraphyses 2–3 μm wide, filamentous, cylindrical, aseptate, unbranched, longer than asci. Asci 48–58 × 7–9 μm (x ̄ = 53 × 8 μm, n = 10), unitunicate, cylindrical, long pedicellate, apically rounded, with a J +, apical ring (rarely seen). Ascospores 21–27 × 10–14 μm (x ̄ = 24 × 12 μm, n = 30), uniseriate, hyaline when immature, dark brown at maturity, equilateral ellipsoidal to broadly fusoid, unicellular, guttulate, with a spiral germ slit over the whole spore length. 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 reached 1–1.5 cm diam. After five 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, Nang Lae village , on decaying branch of Saraca sp. ( Fabaceae ), 18 March 2024, Achala Rathnayaka, AA 13 ( MFLU 24-0529 , holotype); ex-type living culture, MFLUCC 24-0611 .

Notes.

Based on the multi-gene phylogeny (ITS, rpb 2, and β-tub), our collections ( MFLU 24-0529 and MFLUCC 24-0611 ) formed a distinct lineage sister to S. quisquiliarum ( YMJ 172 ) with 90 % ML bootstrap and 0.98 PP support (Fig. 10 ). Stilbohypoxylon chiangraiense shares morphologies similar to the Stilbohypoxylon genus by having superficial, solitary, globose stromata, cylindrical asci with a J +, apical ring; and brown, ellipsoidal ascospores with a spiral germ slit. However, asci are very rarely observed in S. chiangraiense . Stilbohypoxylon quisquiliarum differs from our fungal collection in that its yellow scales turn brown when mature, which are present on the stromata. In addition, our fungal collection has shorter ascospores (21–27 μm) than S. quisquiliarum (27.5–28.5 μm) ( Petrini 2004). The base pair differences between S. chiangraiense ( MFLUCC 24-0611 ) and S. quisquiliarum ( YMJ 172 ) are as follows: ITS = 1.9 % (11 / 578), β-tub = 11.9 % (123 / 1033). Considering the morpho-molecular data analysis, we established S. chiangraiense as a new species in Stilbohypoxylon .

Figures

Figure 10. Phylogram generated from ML analysis based on the combined dataset of ITS, rpb 2, and β-tub. The tree is rooted to Hypoxylon fragiforme (HAST 383 and MUCL 51264). 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 12. Stilbohypoxylon chiangraiense on the dead branch of Saraca sp. (MFLU 24-0529, Holotype). a. Substrate; b, c. Appearance of stromata on the host, showing yellow scales (arrows indicating yellow scales); d, e. A horizontal section through a stroma; f. Peridium; g. Paraphyses; h, i. Immature asci; j. Apical apparatus stained in blue with Melzer’s reagent; k – m. Ascospores; n, o. Ascospores with a germ slit (arrows indicating a spiral germ slit); p, q. Colony on the PDA (p upper, q lower). Scale bars: 1 mm (b); 500 μm (c); 200 μm (d, e); 20 μm (g – j); 10 μm (f, k – o).