Pluteus tenuipileus Z. X. QI, B. Zhang & Y. Li, 2025

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 tenuipileus Z. X. QI, B. Zhang & Y. Li sp. nov.

Figs 5 A – D , 8

Etymology.

The species epithet “ tenuipileus ” (Latin) refers to the thin, flake-like pileus.

Diagnosis.

Morphologically similar to P. lauracearum , differing by its smooth and thin pileus, distinct ITS sequences (genetic distance = 0.021, SE = 0.006), and distribution in East Asia ( China).

Holotype.

CHINA • Jilin Province, Cold Jungle National Nature Reserve ; 11 August 2021, G. Rao, FJAU 66591 (ITS: PP 516621 , LSU: PP 516671 , tef 1: PP 551607 ) (Collection no.: Rao 1325).

Description.

Basidiomata medium-sized. Pileus 17–33 mm diam; plano-convex, sometimes slightly depressed at the center; light grayish brown (2.5 YR 7 / 2) with white margins (2.5 YR 9 / 2); surface smooth to rarely white pruinose (2.5 YR 9 / 2), radial striate from the middle to the margin; margin pilcate, with umbrella-like teeth. Lamellae cream to flesh-pink (2.5 R 9 / 2–2.5 R 9 / 6), free, crowded, thick, unequal, ventricose, 3–5 mm wide, with even edges; lamellar edge white. Stipe 20–25 × 2–3 mm, cylindrical, white (2.5 R 9 / 2), base bulbous, fibrous and brittle bony, surface with white pruinose (2.5 R 9 / 2). Odorless. Spore prints pink.

Basidiospores [120, 3, 2] 6.0–7.0 × 5.0–6.0 (– 6.5) μm, avL × avW = 6.4–6.6 × 5.5–5.7 µm, Q = 1.07–1.40 μm, avQ = 1.16–1.20 μm, subglobose to broadly ellipsoid or ovoid, slightly pinkish, smooth, thin-walled. Basidia 21–28 × 7–8 µm, clavate, thin-walled, 4 - sterigmate, hyaline. Pleurocystidia 53–93 × 24–32 μm, abundant, scattered, fusiform or subfusiform, apical portion with mucronate, rostrate with up to 2–6 μm long, thin-walled, smooth, hyaline. Lamellar edge sterile. Cheilocystidia 36–68 × 14–26 μm, abundant, clustered, narrowly clavate to clavate, or long clavate, obtusely rounded apically, short basally, thin-walled, hyaline. Pileipellis a trichohymeniderm, with terminal elements 58–95 × 15–30 μm, broadly clavate or fusiform, thin-walled, with brown intracellular pigment. Stipitipellis a cutis, hyphae 3–12 µm diam, cylindrical, hyaline, thin-walled. Caulocystidia 24–53 × 7–17 μm, numerous, occurring in clusters, cylindrical to broadly clavate to broadly fusiform, or narrowly utriform, hyaline, thin-walled. Clamp connections absent in all tissues.

Habitat.

Solitary on decaying wood in coniferous forests.

World distribution.

China.

China distribution.

Jilin Province.

Additional specimens examined.

CHINA • Jilin Province, Cold Jungle National Nature Reserve ; Solitary on rotting wood in mixed forests; 2 August 2020, G. Rao, FJAU 66592 (Collection no.: Rao 927) (ITS: PP 516620 , LSU: PP 516670 , tef 1: PP 551606 ) .

Notes.

Pluteus tenuipileus is characterized by a pileus thinly, with a furrowed stripe along the margin. The fruiting bodies are brittle, and the pleurocystidia are apically mucronate or rostrate.

Morphologically, P. tenuipileus shares features with P. lauracearum , P. boudieri , and P. semibulbosus , but can be distinguished from each based on several characteristics. P. tenuipileus differs from P. lauracearum by its smooth pileus and smaller basidiospores (avL × avW = 6.4–6.6 × 5.5–5.7 µm), whereas P. lauracearum exhibits a pruinose or distinctly granulose pileus surface with larger basidiospores (avL × avW = 7.3 × 6.0 µm). Additionally, P. tenuipileus is distributed in East Asia ( China), while P. lauracearum occurs in Eurasia ( Turkey and Portugal) ( Kaygusuz et al. 2019), with an ITS genetic distance of 0.021 (SE = 0.006). P. tenuipileus can be separated from P. boudieri by pileipellis structure: trichohymeniderm in the former versus monostratous hymeniderm in the latter ( Vellinga and Schreurs 1985; Orton 1986). P. semibulbosus was originally described as a small whitish species characterized by a softly atomate, sulcate pileus and pubescent stipe with a distinctly bulbous base ( Fries 1838). Lasch (in Fries 1838) did not provide basidioma dimensions, although Saccardo (1887: 674) documented a pileus 13 mm in width and stipe 25 mm in length. Despite numerous descriptions of this species in contemporary literature ( Yang 2011; Xu 2016; Kaygusuz et al. 2019; Malysheva et al. 2023), the absence of corresponding type specimens and the lack of clear phylogenetic placement has necessitated the adoption of a broad concept of P. semibulbosus . Ševčíková (2020) and Justo et al. have indicated that this broad morphological species concept corresponds to a polyphyletic group (unpublished data) and that further studies, including the designation of a type specimen for P. semibulbosus , are required. Even within this broad conceptual framework, P. semibulbosus can be distinguished from P. tenuipileus primarily based on the quantity and morphology of pleurocystidia, while the exceptionally thin pileus serves as a more diagnostic feature of P. tenuipileus ( Singer 1986).

When comparing P. tenuipileus with taxa that produce notably smaller basidiomata, such as P. candidus and P. stylobates , several distinctive morphological features become taxonomically significant. P. tenuipileus differs from P. candidus in having a wider pileus (17–33 mm) with radiating stripes, whereas P. candidus has smaller basidiomata (10 mm) lacking striations ( Saccardo 1887). Similarly, P. tenuipileus can be differentiated from P. stylobates by its smooth to rarely white- pruinose surface, wider pileus (17–33 mm), and bulbous stipe base, in contrast to the smaller pileus (≤ 10–15 mm) with dark squamules on the surface and distinctive discoid stipe base characteristic of P. stylobates ( Velenovský 1921) .

Figures

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 8. A. Macroscopic characteristics of Pluteus tenuipileus. B. Basidiospores. C. Caulocystidia. D. Cheilocystidia. E. Pileipellis elements. F. Pleurocystidia. Scale bars: 0.5 cm (A); 10 µm (B, F); 20 µm (C, D, E).