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

Figs 7 D, E , 13

Etymology.

The species epithet “ hinnuleus ” (Latin): refers to the clay-buff to earthy yellow pileus color.

Diagnosis.

Pluteus hinnuleus differs from P. albivillus by its clay-buff to earthy yellow pileus color, small basidiospores, pleurocystidia with 1–7 μm finger-like projections on the apex. It grows preferentially in birch forests ( Betula ) on decaying wood branches and is distributed in Northeast China. The ITS genetic distance is 0.125 (SE = 0.017).

Holotype.

CHINA • Heilongjiang Province, Shuanghe National Nature Reserve , 12 July 2019, D. Z. Guo, FJAU 66614 (ITS: PQ 810768 , LSU: PQ 810746 , tef 1: PQ 811064 ) (Collection no.: Guo 377).

Description.

Basidiomata medium-sized. Pileus 34 mm diam; convex to slightly hemispherical; clay-buff to earthy yellow (2.5 Y 8 / 6), dry, the surface with recurved squamules, the central scales color dark brown (10 YR 4 / 6), the margin slightly inflexed. Lamellae free, 3–5 mm wide, moderately crowded, thick, pink (2.5 YR 7 / 4), unequal, slightly ventricose, edges even or flocculose; lamellar edge concolorous to the sides. Stipe 43 × 4–7 mm, fibrous, solid, earthy yellow (2.5 Y 8 / 6), with brown glandular dots on the surface (7.5 YR 4 / 2), slightly inflated at the base. Spore print pink.

Basidiospores [50 / 1 / 1] 6.5–7.5 (– 8.0) × (– 5.0) 5.5–6.5 (– 7.0) µm, avL × avW = 6.8–7.2 × 5.7–6.0 µm, Q = 1.16–1.33 µm, avQ = 1.20–1.25 µm, mostly subglobose, broadly ellipsoid to ellipsoid, smooth, slightly pinkish, thin-walled. Basidia 25–34 × 9–11 μm, clavate, thin-walled, 4 - sterigmate, hyaline. Pleurocystidia 60–93 × 20–35 μm, abundant, scattered, two forms, one broadly fusiform with bluntly rounded apices, the other narrowly fusiform with a longer neck and unequal apical rostrate, long projection 3–7 μm long, thin-walled, smooth, hyaline. Lamellar edge sterile. Cheilocystidia 43–78 × 15–24 μm, clustered, numerous, broadly clavate to clavate, apically obtuse, partly with brown intracellular pigment, thin-walled, smooth. Pileipellis a hymeniderm, with terminal elements 81–155 × 19–33 μm, broadly clavate or broadly cylindrical, thin-walled, with brown intracellular pigment. Stipitipellis a cutis, hyphae 4–6 μm diam, cylindrical, hyaline, thin-walled. Caulocystidia 31–51 × 15–25 μm, clustered, long clavate, apically obtusely rounded, with brownish intracellular pigment, smooth, thick-walled. Clamp connections absent in all tissues.

Habitat.

Solitary on decaying wood in birch forests ( Betula platyphylla Sukaczev ).

World distribution.

China.

China distribution.

Heilongjiang Province.

Notes.

Pluteus hinnuleus is primarily characterized by its dry pileus surface bearing recurved squamules, clay-buff to earthy yellow coloration, and ecological preference for rotting wood in B. platyphylla forests.

Morphologically, P. hinnuleus resembles P. albivillus , with both species exhibiting hemispherical pileus and firm, fibrous stipes. However, these taxa can be differentiated by basidiospore dimensions, pleurocystidia morphology, and substrate ecology. P. hinnuleus produces smaller basidiospores (avL × avW = 6.8–7.2 × 5.7–6.0 µm) with pleurocystidia featuring 1–7 μm finger-like apical projections, and occurs on decaying wood in Betula platyphylla forests. In contrast, P. albivillus forms larger basidiospores (avL × avW = 7.3–7.6 × 5.8–6.0 µm) with pleurocystidia lacking apical projections, and is associated with decaying wood in Larix sibirica forests.

Phylogenetically, P. hinnuleus is closely related to P. dianae and P. aff. dianae , though morphologically distinct from both. P. hinnuleus differs from P. dianae by its slightly smaller basidiospores (avL × avW = 6.8–7.2 × 5.7–6.0 µm versus avL × avW = 7.2 × 6.3 µm in P. dianae ), with an ITS genetic distance of 0.041 (SE = 0.009) supporting this separation. Similarly, P. hinnuleus is distinguished from P. aff. dianae by its larger basidiospores (avL × avW = 6.8–7.2 × 5.7–6.0 µm versus avL × avW = 6.6 × 5.3 µm in P. aff. dianae ) and geographic distribution in East Asia ( China) rather than Europe ( Spain). This distinction is further supported by an ITS genetic distance of 0.047 (SE = 0.010).

Figures

Figure 7. Basidiomata features. A – C. Pluteus ultraputripiceae (A. FJAU 66611, B, C. FJAU 66594). D, E. P. hinnuleus (FJAU 66614). A – C. Photos by Zheng-Xiang Qi. D, E. Photos by Di-Zhe Guo. Scale bars: 1 cm.

Figure 13. A. Macroscopic characteristics of Pluteus hinnuleus. B. Basidiospores. C. Caulocystidia. D. Basidia and Pleurocystidia. E. Pleurocystidia. F. Cheilocystidia. G. Pileipellis elements. Scale bars: 1 cm (A); 10 µm (B – F); 20 µm (G).