Skeletocutis cangshanensis B.K. Cui & Shun Liu, sp. nov.
Index Fungorum number: IF 559465; MycoBank number: MB 559465; Facesoffungi number: FoF 10674; Figs. 1a, 2
Differs from other Skeletocutis species by its white pore surface when fresh, white to buff-yellow upon drying, small and circular to angular pores (7–10 per mm), and cylindrical basidiospores (2.7–3.5×0.8–1.5 μm).
Etymology – Cangshanensis (Lat.): refers to the type locality (Cangshan Park) of the type specimen.
Holotype – Cui 17978.
Fruiting body. Basidiocarps annual, resupinate, not easily separated from substrate, soft leathery, without odour or taste when fresh, becoming corky upon drying, up to 8.5 cm long, 3.5 cm wide, and 1 mm thick at center. Pore surface white when fresh, becoming white to buff-yellow upon drying; pores circular to angular, 7–10 per mm; dissepiments thick, entire. Subiculum white, corky, up to 0.2 mm thick. Tubes darker than poroid surface, corky, up to 0.5 mm long.
Hyphal Structure. Hyphal system dimitic; generative hyphae with clamp connections, hyaline, thin- to slightly thick-walled, dominant at dissepiment edge; skeletal hyphae thick-walled with a wide to narrow lumen; IKI–, CB–, unchanged in KOH.
Subiculum. Generative hyphae frequent, hyaline, thinto slightly thick-walled, rarely branched and bearing fine crystals, 1.5–2.8 μm in diameter; skeletal hyphae dominant, thick-walled with a narrow lumen, flexuous, unbranched, interwoven, 2–3.5 μm in diameter.
Tubes. Generative hyphae frequent, thin-walled, frequently branched, usually covered by fine crystals, sharply pointed encrustations, especially at dissepiment edge, 1.5–2.5 μm in diameter; skeletal hyphae dominant, thick-walled with a wide to narrow lumen, occasionally branched, subparallel along the tubes, not agglutinated, 2–3 μm in diameter. Dissepiment edge dimitic with smooth skeletal hyphae, and dominant winding, encrusted generative hyphae. Cystidia absent, cystidioles abundant, bottle-shaped, with a conical apex, 7.5–17 × 3.2–4.7 μm. Basidia clavate, with a basal clamp connection and four sterigmata, 9.6–13.5 × 3.2–4.7 μm; basidioles in shape similar to basidia, but slightly smaller.
Spores. Basidiospores cylindrical, hyaline, thin-walled, smooth, IKI–, CB–, (2.6–)2.7–3.5 × 0.8–1.5 μm, L=3.02 μm, W =1.02 μm, Q =2.76–3.23(n=90/3).
Material examined – China, Yunnan Province, Dali, Cangshan Park, on angiosperm stump, 4 November 2019, Cui 17978 (holotype, BJFC).
Additional specimens examined – China, Yunnan Province, Dali, Cangshan Park, on fallen angiosperm branch, 4 November 2019, Cui 17990, 17994 (Paratypes, BJFC).
GenBank numbers – Cui 17978—MZ327279 (ITS), MZ348535 (LSU), Cui 17990—MZ327280 (ITS), MZ348536 (LSU). Cui 17994—MZ327281 (ITS), MZ348537(LSU).
Notes – In the phylogenetic tree, the three specimens of Skeletocutis cangshanensis formed a highly supported lineage (Fig. 3), and grouped together with S. bambusicola L.W. Zhou & W.M. Qin. Morphologically, both S. cangshanensis and S. bambusicola have similar pores, but S. bambusicola differs by having wider basidiospores (2.5–3 × 1.5–2 μm) and growth on Bambusa (Zhou and Qin 2012). Skeletocutis lepida A. Korhonen & Miettinen, S. mopanshanensis C.L. Zhao and S. yunnanensis L.S. Bian, C.L. Zhao & F. Wu were also discovered from Yunnan Province. Skeletocutis lepida differs from the new species by having narrower basidiospores (2.9–3 × 0.5–0.6 µm; Korhonen et al. 2018); S. mopanshanensis differs by having larger pores (4–5 per mm) and basidiospores (4.7–6.6 × 3.2–4.5 µm; Wu et al. 2017); S. yunnanensis differs by having larger pores (5–6 per mm) and basidiospores (3.4–4.5 × 1–1.2 µm; Bian et al. 2016).
Figure 1 – Basidiocarps of Skeletocutis species. a. S. cangshanensis; b. S. subchrysella (scale bars: a, b=2 cm)
Figure 2 – Microscopic structures of Skeletocutis cangshanensis (drawn from the holotype). a. Basidiospores; b. Basidia and basidioles; c. Cystidioles; d. Section of dissepiment edge; e. Hyphae from trama; f. Hyphae from subiculum. Scale Bars: a=5 µm; b–f=10 µm
Figure 3 – Maximum likelihood tree illustrating the phylogeny of Skeletocutis based on the combined sequences dataset of ITS+nLSU. Branches are labeled with maximum likelihood bootstrap higher than 50%, parsimony bootstrap proportions higher than 50% and Bayesian posterior probabilities more than 0.90 respectively. Bold names = New species