Occultibambusa clavata W.P. Wang, H.W. Shen, K.D. Hyde & Z.L. Luo, in Wang, Hyde, Bao, Wanasinghe, Lin, Shen, Lu, Zhang, Su, Li, Al-Otibi, Yang & Luo, Mycosphere 15(1): 6560 (2024)

Index Fungorum number: IF902424; MycoBank number: MB902424; Facesoffungi number: FoF16097

Etymology – Referring to the clavate asci of this fungus.

Holotype – HKAS 131377

Saprobic on submerged stem of Bambusoideae. Asexual morph: Undetermined. Sexual morph: Ascomata 210–350 µm diam, 190–260 µm high., scattered, semi-immersed, visible as black ellipsoidal on host surface, uniloculate, flat spheroids. Ostiole papillate, central, cylindrical, periphysate. Peridium 9.3–50 µm thick, thinning around the ostiole, cortex of host, coriaceous, consisting of several layered pale brown to brown, irregular or nearly oval cells of textura angularis. Hamathecium composed of dense, 1.8–4 µm wide, subcylindrical, hyaline to brown, transversely septate, branched pseudoparaphyses. Asci 60–130 × 17–21 µm (x̅ = 86.1 × 19.1 µm, n = 15), 8-spored, bitunicate, fissitunicate, clavate, slightly curved, mostly with a short pedicel or elongated after discharge (up to 60 µm long), broadly rounded apical with an ocular chamber. Ascospores 25– 31 × 6.4–8.7 µm (x̅ = 28.1 × 7.5 µm, n = 30), overlapping, biseriate, hyaline when young, pale olive when mature, fusiform with acute ends, straight or slightly curved, apical cell slightly larger than the basal cell, mostly uniseptate, septate central, slightly constricted at the septum, guttulate, smooth-walled.

Culture characteristic – Ascospores germinating on PDA within 12 h, and germ tubes produced from both ends. Colonies on the malt extract agar (MEA) reaching 25 mm diameter after 3 weeks at room temperature. Mycelium dry, dense, colonies on the surface of MEA, with regular edges, velvety, white. Reverse circular, brown to dark brown, with white edges, smooth.

Material examined – China, Yunnan Province, Wenshan Zhuang and Miao Autonomous Prefecture, Bamei Town, on submerged dead stem of Bambusoideae species, 7 February 2022, W.P. Wang, S-3263 (HKAS 131377, holotype), ex-type living cultures CGMCC 3.25424 = KUNCC 23– 14577.

Notes – In the phylogenetic analysis, Occultibambusa clavata (CGMCC 3.25424) constitutes an independent lineage that is basal to O. aquatica, O. bambusae, O. chiangraiensis, O. jonesii, O. kunmingensis and O. pustula with 100% ML/1.00 PP support (Fig. 2). Occultibambusa clavata has larger ascospores than O. aquatica, O. bambusae, O. chiangraiensis and O. pustula (Dai et al. 2017, Hyde et al. 2016b, Jiang et al. 2021a). Occultibambusa clavata differs from O. jonesii in having a thin peridium around the ostiole and shorter but broader ascospores (25–31 × 6.4–8.7 vs. 27–33.5 × 5.5–6.5 µm) (Zhang et al. 2017a). Occultibambusa clavata has a dense hamathecium and shorter asci (60–130 × 110–140 (–160) µm) with broad rounded apices, which is different from O. kunmingensis (Dong et al. 2020). We therefore identify O. clavata as a new species.

Figure 1 – Occultibambusa clavata (HKAS 131377, holotype). a, b Ascomata on the substratum. c, d Vertical section of ascomata. e Structure of ostiole and peridium. f Hamathecium. g–j Asci. k–n Ascospores. o Germinating ascospore. p, q Colony on MEA from surface and reverse. Scale bars: c, d = 50 µm, e = 30 µm, f–i = 15 µm, j = 20 µm, k–o = 10 µm.

Figure 2 – RAxML tree based on analysis of Occultibambusa that combined LSU, SSU, tef1-α, ITS, and rpb2 dataset. The combined analyses include 18 strains with 4302 characters, including gaps (LSU: 853 bp, SSU: 986 bp, tef1-α: 930 bp, ITS: 566 bp, and rpb2: 967 bp). Bootstrap support values for maximum likelihood (ML) greater than 75% and Bayesian posterior probabilities greater than 0.95 are indicated above branches as ML/PP. The tree is rooted with Seriascoma didymosporum (MFLUCC 11–0179) and S. yunnanense (MFLU 19–0690). The new collection is indicated in red. Ex-type strains are indicated with “T” after the strain number.