Hypoxylon thailandicum

Hypoxylon thailandicum Rathnayaka, K.D. Hyde & Chethana, MycoKeys 120:35-117 (2025)

Index Fungorum number: IF903885; Facesofungi number: FoF00373

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 (x̄ = 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 (x̄ = 80 × 9.4 µm, n = 15), 8-spored, unitunicate, cylindrical, pedicellate, with an inamyloid, apical ascal apparatus. Ascospores 13–18 × 7–10 µm (x̄ = 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, AA06 (MFLU 24-0530, holotype); ex-type living culture, MFLUCC 25-0024.

GenBank numbers: PV468231 (LSU), PQ164172 (ITS), PV476728 (rpb2), PV469696 (β-tub)

Notes: In multi-gene phylogeny (ITS, LSU, rpb2, and β-tub), our novel isolates (MFLU 24-0530 and MFLUCC 25-0024) formed a separate lineage sister to H. begae (S99 and YMJ 215) and H. blackburniae (BRIP 72467b) with 97% ML bootstrap and 0.95 PP support. 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 72467b), 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 72467b). Additionally, the absence of rpb2 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.