Clitopilus baronii Consiglio & Setti, Index Fungorum 427: 1. 2019. Figs 3 a – d, 4 a – c, 6 a – c Description. Basidiomata pleurotoid to crepidotoid, small size. Pileus 3–15 mm wide, convex then expanded; surface yellowish-white (# 9 a 8 a 7 a), greyish (# a 6 a 39 f) to bluish-grey (# 6 a 757 b), usually subtly woolly-tomentose at the base then reduced to border; margin slightly incurved, even, sometimes faintly striated; context less than 1 mm thick. Lamellae whitish (# a 9 a 7 a 8) to yellowish (# 9 d 896 d), sometimes hygrophanous, slightly dense or crowded, edges entire and concolorous, lamellulae numerous. Stipe absent; the base with white (# e 9 ebed) mycelium. Odour none. Basidiospores (6) 6.5–9.5 (11) × 4–5 (5.5) μm, L m × W m = 7.5 (± 1.01) × 4.5 (± 0.35) μm, Q = 1.4–1.98 (Q avg = 1.66 ± 0.14) [43 / 2 / 2], hyaline, ellipsoid to fusiform, subovoid in profile and face view, slightly angled in polar view with 8–10 inconspicuous or obscure longitudinal ridges in total. Basidia 17.5–24 × 6.5–9 μm, clavate, hyaline, 2 - or 4 - spored; sterigmata 3–5.5 μm. Lamellar trama subregular, composed of thin-walled, hyaline, cylindrical hyphae with a diameter of 2.5–9 μm. Lamellae edges fertile. Pleurocystidia and cheilocystidia absent, but occasionally forming a few cylindrical tramal hyphae with a diameter of 2–3 μm over the edge. Pileus context about 150–200 μm thick. Pileipellis a cutis composed of compactly arranged, thin-walled, hyaline, smooth, cylindrical hyphae with a diameter of 3.5–9 μm, featuring sparely arranged and erect hyphae with a diameter of 2–3 μm; pileal trama subregular or irregular, composed of hyaline, filamentous, thin-walled hyphae, with a diameter of 2.5–8.5 μm. Clamp connections absent. Ecology and distribution. Lignicolous, scattered or gregarious on rotten wood in the mixed broadleaf forest, distributed in Jiangsu Province, China, in May. Additional specimens examined. China • Jiangsu Province, Nanjing City, Zijinshan, alt. 42 m, scattered or gregarious on rotten wood (Quercus sp.), in the mixed broadleaf (i. e. Quercus acutissima, Quercus aliena, Celtis sinensis, Liquidambar formosana and Cunninghamia lanceolata) forest, 7 May 2023, collected by X. Chen, CX 119 (KUN-HKAS 145333); same places, alt. 38 m, scattered on rotten wood (Quercus sp.), in the mixed broadleaf (Quercus glauca, Pterocarya stenoptera, Ilex chinensis, Cunninghamia lanceolata, Ilex cornuta, Liquidambar formosana and Ligustrum lucidum) forest, 9 May 2023, collected by X. Chen, CX 134 (KUN-HKAS 145334). Notes. Clitopilus baronii belongs to C. sect. Scyphoides (Fig. 1). In the original description, this species was found growing on a decaying trunk of Quercus sp. It is characterised by its sessile basidiomata, orbicular to conchate white pileus, cream-rose lamellae, ellipsoidal to subamygdaliform basidiospores with 8–10 obscure longitudinal ridges and lageniform cheilocystidia. The macro- and microscopic features of our specimens (KUN-HKAS 145333 & 145334) closely match those described in the primary literature (Consiglio and Setti 2019). However, we did not observe any lageniform cheilocystidia in our specimens; we only identified a few thin cylindrical tramal hyphae over the edge. This observation aligns with findings by Noordeloos (1984) regarding C. daamsii, particularly in some older specimens. In our previous study, we also noted this phenomenon of thin cylindrical tramal hyphae at the edge in C. crispus Pat. However, this occurrence was generally casual and rare. In the phylogenetic tree of Clitopilus, we could discover some unusual results regarding C. baronii. In the combined multigene analyses (ITS - LSU - RPB 2 - TEF 1), our specimens were found to separate from the clades of C. baronii and grouped (BS / PP = 69 / 1) closer to C. pinstus (G. Immerzeel 1990-11). When we compared the different genes separately between our samples and holotype of C. baronii (AMB 18363), we found that our samples exhibited over 99 % similarity in ITS region. However, the similarity was only about 90 % for both RPB 2 and TEF 1. For ITS, we have tested them several times in different companies, but all yielded consistent results. Regarding RPB 2 and TEF 1, we did not detect any issues with the original data; all sequences were bidirectionally sequenced to ensure unimodality and were matched by hand in software. Considering the macro- and microscopic features, we tentatively classified our specimens as Clitopilus baronii. More samples are needed to resolve our uncertainties regarding both the presence of cheilocystidia and the phylogenetic relationship.

Published as part of Jian, Sipeng, Chen, Xia, Yang, Tianwei, Xu, Xinjing, Gao, Feng, Fang, Yiwei, Liu, Jing & Zhang, Chunxia, 2025, Biotrophic and saprophytic fungi from the Rhodocybe - Clitopilus clade (Entolomataceae): two new species and one now record in subtropical China, pp. 227-254 in MycoKeys 116 on pages 227-254, DOI: 10.3897/mycokeys.116.148775