Pluteus aff. semibulbosus

Qi, Zheng-Xiang, Wang, Li-Bo, Qian, Ke-Qing, Shi, Li-Li, Hu, Jia-Jun, Tuo, Yong-Lan, Rao, Gu, Samwel Jacob, Muharagi, Liu, Rui-Peng, Liu, Ming-Hao, Guo, Di-Zhe, Liu, Ya-Jie, Zhang, Bo, Li, Xiao & Li, Yu, 2025, Integrating morphology, phylogeny, substrate, and distribution: clarifying the major phylogenetic framework of Pluteus sect. Hispidoderma (Agaricales, Pluteaceae) and describing 18 species, IMA Fungus 16, pp. e 154329-e 154329 : e154329-

Pluteus aff. semibulbosus

Figs 5 J, K , 11

Description.

Basidiomata medium-sized. Pileus 43 mm diam; hemispherical; charred yellow in the center, transitioning to light yellow (10 YR 9 / 2) to white (10 P 9 / 2) toward the margin; surface dry, or dehisce, slightly velvety; margin shorter grooves striate, and straight. Context pale yellow (2.5 Y 9 / 2). Lamellae free, 4–8 mm wide, crowded, white (10 P 9 / 2) to yellowish (2.5 Y 9 / 2), unequal, thin, ventricose, edges even or flocculose; lamellar edge white. Stipe 39 × 4 mm, fibrous, hollow, clavate, slightly curved at the base and inflated bulbous, with white mycelium close to the rotting wood, overall pale yellow (10 YR 9 / 2) with white (10 P 9 / 2) glandular dots on the surface. Spore print unknown.

Basidiospores [40 / 1 / 1] 7.0–8.0 (– 8.5) × 6.0–6.5 (– 7.5) µm, avL × avW = 7.4–7.6 × 6.2–6.5 µm, Q = 1.07–1.21 µm, avQ = 1.10–1.15 µm, globose to subglobose, rarely broadly ellipsoid, smooth, slightly pinkish, thin-walled. Basidia 24–33 × 9–11 µm, clavate, thin-walled, 4 - sterigmate, hyaline. Pleurocystidia 53–80 × 15–35 μm, rare, scattered, fusiform to broadly subfusiform, or broadly clavate, apically obtuse, thin-walled, smooth, hyaline. Lamellar edge sterile. Cheilocystidia 33–61 × 12–18 μm, abundant, clustered, clavate or subfusiform, apically obtuse, thin-walled, hyaline. Pileipellis a hymeniderm, with terminal elements 70–105 × 18–29 μm, broadly subcylindric or subfusiform, thin-walled, with pale brown intracellular pigment. Stipitipellis a cutis, hyphae 4–6 μm diam, cylindrical, hyaline, thin-walled. Caulocystidia 43–73 × 12–22 μm, scattered to clustered, abundant, composed of clavate, fusiform, and broadly fusiform, most with bluntly rounded apices, a few with small apical projections, some containing brownish intracellular pigment, thin-walled, smooth. Clamp connections absent in all tissues.

Habitat.

Solitary on very rotten decaying wood in broad-leaved forests ( Q. mongolica ).

World distribution.

China.

China distribution.

Jilin Province.

Additional specimens examined.

CHINA • Jilin Province, Cold Onion Ridge Forest Park ; 43°02'2.09"N, 127°58'77.59"E; Scattered on very rotten decaying wood in broad-leaved forests ( Q. mongolica ); 5 August 2021, G. Rao, FJAU 66617 (Collection no.: Rao 1285) (ITS: PQ 810766 , LSU: PQ 810744 , tef 1: PQ 811050 ) .

Notes.

The Chinese specimens described here share morphological similarities with P. semibulbosus sensu lato, including the bulbous stipe base, subglobose spores, and fusiform pleurocystidia. However, P. semibulbosus lacks a clear taxonomic delimitation, as noted by Ševčíková (2020) and Justo et al. (unpublished), who indicated that this taxon represents a polyphyletic group requiring further study.

In our phylogenetic analysis, the Chinese specimens formed a strongly supported clade (MLB = 100, BPP = 1, Fig. 2 ) with the Japanese specimen TNSF 12393 (labeled as P. aff. semibulbosus ). Although TNSF 12393 lacks morphological description, the molecular evidence suggests these specimens represent the same taxonomic entity. As shown in Table 3 , our material can be distinguished from the closely related P. jilinensis and P. spaniophyllus by its larger basidiomata (pileus 43 mm), hemispherical pileus shape, and distinctive caulocystidia with small apical projections.

Given the uncertain status of P. semibulbosus sensu lato and pending a comprehensive revision of this species complex, we provisionally treat our specimens as P. aff. semibulbosus until further taxonomic resolution is achieved.

Figures

Figure 2. Phylogenetic tree of the / plautus clade of the sect. Hispidoderma. The best tree from the ML and BI analysis of the ITS + tef 1 dataset. The two values of internal nodes respectively represent the Maximum Likelihood bootstrap (MLBP) / Bayesian posterior probability (BIPP). Nodes with a bootstrap probability (BP) ≥ 80 and a Bayesian posterior probability (PP) ≥ 0.80 are indicated in the phylogram. This study species is in bold and red font.

Figure 5. Basidiomata features. A – D. Pluteus tenuipileus (A, B. FJAU 66591, C, D. FJAU 66592). E – G. P. jilinensis (FJAU 66616). H – I. P. spaniophyllus (FJAU 66593). J, K. P. aff. semibulbosus (FJAU 66617). A – K. Photos by Gu Rao. Scale bars: 1 cm.

Figure 11. A. Macroscopic characteristics of Pluteus aff. semibulbosus. B. Basidiospores. C. Cheilocystidia. D. Basidia and Pleurocystidia. E. Pleurocystidia. F. Caulocystidia. G. Pileipellis elements. Scale bars: 1 cm (A); 5 µm (B); 10 µm (C – G).