Hypoxylon omphalostiolatum P. C. Ding, Madhushan & Maharachch., 2025

Ding, Peng-Cheng, Madhushan, Asanka, Samarakoon, Milan C., Liu, Jian-Kui & Maharachchikumbura, Sajeewa S. N., 2025, A new species of Hypoxylon (Hypoxylaceae, Xylariales) from Sichuan Province, China, Phytotaxa 715 (3), pp. 229-244 : 238-239

Hypoxylon omphalostiolatum P. C. Ding, Madhushan & Maharachch. , sp. nov. ( FIGURE 2 )

MycoBank: 859931

Etymology: The name reflects the umbilicate ( omphalos) ostioles ( ostiolatum).

Saprobic on the decaying branches of an unidentified plant. Sexual morph: Stromata superficial, pulvinate to effused-pulvinate, and gregarious, with inconspicuous perithecial mounds, surface violet-brown, multi-layered perithecial mounds, spreading over a large area of the host surface, yellow pigments in 10% KOH. Perithecia (= 229 × 204 μm, n = 10) globose to ellipsoid, with an ostiole. Ostioles inconspicuous, umbilicate, usually overlain with conspicuous white substance. Peridium 22–69 μm (= 46.3 μm, n = 20) wide, multi-layered, outer layer dark purple with thick-walled cells of textura angularis, inner layer hyaline with thin-walled cells of angularis and prismatica. Paraphyses 2–9 μm (= 6.68 μm, n = 30) wide, septate, unbranched, hyaline, cellular, minutely guttulate, and embedded in a gelatinous matrix. Asci 84–132 × 6–12 μm (= 106.23 × 8.51 μm, n = 30), ascospore bearing part 56–85 μm (= 70.5 μm, n = 30), non-bearing part 33–48 μm (= 39.4 μm, n = 30), 8-spored, unitunicate, cylindrical or clavate, and long-pedicellate, J- apical ring in Melzers’reagent. Ascospores 7–12 × 3–7 μm (= 9.45 × 5.2 μm, n = 50), uniseriate, ellipsoidal, narrow at both ends, smooth-surfaced, aseptate, initially hyaline to yellowish brown, dark brown at maturity, and contain 1 or 2 large guttules to multiple small guttules, perispore dehiscent in 10% KOH. Asexual morph: Not observed.

Colony characteristics: Conidia germinate on PDA within 24 h at 24 °C. Colonies on PDA reaching 42 mm in diameter after 3 weeks at 25 °C. Mycelia superficial, surface slightly rough, with undulate margin, forming small, from above, white; reverse, blackish brown.

Materials examined: CHINA, Sichuan Province, Liangshan Yi Autonomous Prefecture , Puge County, Luoji Mountain Town , 27˚42'44'' N, 102˚24'07'' E, 2140 m, unknown host, 20 June 2024, P. C. Ding XCJ4-6-1( HKAS 149990 , holotype), ex-type CGMCC 3.28999 = UESTCC 25.0246 ; ibid., XCJ4-6- 2 paratype ( UESTCC 25.0247 ) .

Notes: In the multi-gene phylogeny, our isolates of H. omphalostiolatum form a sister clade with H. guiyangense (KUNCC 23.15543, KUNCC 23.15546), with (87 ML/ 0.96 BYPP) bootstrap support ( FIGURE 1 ). The BLASTn analysis of H. omphalostiolatum type strain (CGMCC 3.28999) and H. guiyangense (KUNCC 23.15543; type strain) shows 99% identity (508/515 bp, 0 gaps) in ITS, 99% identity (730/734 bp, 3 gaps) in LSU, and 96% identity (942/977 bp, 3 gaps) in tub 2. Also, H. omphalostiolatum (CGMCC 3.28999) and other closely related H. guizhouense (KUNCC 23-15544) shows 98% identity (506/516 bp, 1 gap) in ITS, 99% identity (728/734 bp, 1 gap) in LSU, and 95% identity (941/986 bp, 17 gaps) in tub 2.

Morphologically, the stromata surface of H. omphalostiolatum (CGMCC 3.28999) is dark brick to dark brown, while the stromata of H. guizhouens e and H. guiyangense are violet-brown and yellowish-brown, respectively. Moreover, the former covers a larger area of the host substrate than the latter two. Perithecia of H. omphalostiolatum are larger (229 × 204 μm) than those of H. guiyangense (135 × 143 μm) and H. guizhouense (195 × 203 μm). Meantime, H. omphalostiolatum has inconspicuous, umbilicate ostioles. The asci of H. omphalostiolatum are also longer (84–132 μm) than H. guiyangense (80–100 μm) and H. guizhouense (80–100 μm). Hypoxylon omphalostiolatum resembles type descriptions of H. guiyangense and H. guizhouense , with hyaline to brown, ellipsoidal ascospores ( Dissanayake et al. 2024). However, H. omphalostiolatum ascospores are wider (9.45 × 5.2 μm) compared to H. guiyangense (9.4 × 4.8 μm), but shorter than H. guizhouense (10 × 4.8 μm). In addition, both H. omphalostiolatum and H. guizhouense possess two guttules, whereas H. guiyangense contains more, and the ostiole of H. omphalostiolatum is inconspicuous. H. guiyangense and H. guizhouense were identified on dead twigs of an unidentified host in Guiyang and Guizhou city ( Dissanayake et al. 2024). Based on combined phylogenetic analysis and detailed morphological evidence, we conclude our collection is a new species, H. omphalostiolatum .

Figures

FIGURE 1. Phylogram of Hypoxylon inferred from combined ITS, LSU, rpb2, and tub2 loci. The tree is rooted to Xylaria hypoxylon CBS 122620 and X. arbuscula CBS 126415. Numbers at the nodes are RAxML bootstrap ≥ 75 % and MrBayes posterior probability ≥ 0. 95. Isolates from type strains are marked with an asterisk. The isolates from the present study are indicated in red bold.

FIGURE 2: Hypoxylon omphalostiolatum (HKAS 149990, holotype) a Fungal specimen b, c Stromata on the host substrate; d section of a stroma; e Peridium; f Paraphyses; g–k Asci; l–q Ascospores (p = Ascospore in 10% KOH, q = germinated ascospore); r KOH-extractable pigments; s, t colony on PDA. Scale bars: 100 µm (d); 20 µm (e); 10 µm (f–k, q); 5µm (l–p).