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

Figs 18 A – C , 19

Etymology.

The species epithet “ costatus ” (Lat.) refers to the ribbed ( costatus ) pileus, characterized by prominent veins, with a distinctly pronounced middle vein.

Diagnosis.

Morphologically similar to P. ornatus , differing in its unstriped pileus margins, smaller basidiospores avL × avW = 6.2–6.5 × 5.2–5.5 µm, and their ITS genetic distance is 0.029 (SE = 0.007). It grows in coniferous forests with decaying wood branches and is distributed in East Asia ( China). Phylogenetically close to P. umbrosus and P. granularis , differing in the lamellae with brown edges.

Holotype.

CHINA • Heilongjiang Province, Shuanghe National Nature Reserve , 13 July 2019, D. Z. Guo, FJAU 66589 (ITS: PP 516603 , LSU: PP 919365 , tef 1: PP 551591 ) (Collection no.: Guo 380).

Description.

Basidiomata medium-sized. Pileus 32–35 mm diam; convex or plano-convex, often with a low, broad umbo; overall silvery gray (5.0 YR 6 / 2), with brown granulose-squamulose or micaceous on the surface, forming a black-brown vein-like stripe (5.0 YR 4 / 10), very dense in the center; veins extended to the margin, gradually less; margin striaght. Lamellae white to light pink (2.5 YR 9 / 2–2.5 R 9 / 6), free, crowded, thick, unequal, 3–5 mm wide, with white to light brown and flocculose edges. Stipe 61–66 × 5–8 mm, cylindrical, hollow, fibrous, brown (5.0 YR 6 / 8), slightly thicker at the base. Odorless. Spore prints pink.

Basidiospores [80, 3, 2] 6.0–6.5 (– 7.0) × 5.0–5.5 (– 6.0) μm, avL × avW = 6.2–6.5 × 5.2–5.5 µm, Q = 1.16–1.40 μm, avQ = 1.20–1.26 μm, broadly ellipsoid to ellipsoid, slightly pinkish, smooth, thin-walled. Basidia 20–28 × 7–9 μm, clavate, thin-walled, 4 - sterigmate, and hyaline. Pleurocystidia 49–95 × 22–33 μm, abundant, scattered, fusiform to flask-shaped, apically obtusely rounded or partially with 1–2 digitiform excrescences at apex, thinly walled, smooth, hyaline. Lamellar edge sterile. Cheilocystidia 41–70 × 16–25 μm, numerous, fusiform to narrowly clavate, or clavate, apically with a mucronate or rostrate, thin-walled, mostly with brown intracellular pigment. Pileipellis a trichohymeniderm composed of narrowed fusiform and clavate elements, terminal elements expanded to a spindle to clavate 62–140 long, 27–36 μm wide, thin-walled, with brown intracellular pigment. Stipitipellis a cutis, hyphae 5–10 µm diam, cylindrical, hyaline, thin-walled. Caulocystidia 53–108 × 11–22 μm, numerous, usually in clusters, spindle, or cylindrical to narrowly lageniform, rounded at apex, with brown to pale brown intracellular pigment, slightly thick and smooth walls. Clamp connections absent in all tissues.

Habitat.

Scattered on decaying wood in coniferous forests ( P. koraiensis ).

World distribution.

China.

China distribution.

Heilongjiang Province, Jilin Province.

Additional specimens examined.

CHINA • Jilin Province, Cold Jungle National Nature Reserve ; Solitary on rotting wood in coniferous forests; 2 August 2020, G. Rao, FJAU 66618 (Collection no.: Rao 938) (ITS: PQ 810769 , LSU: PQ 810757 , tef 1: PQ 811052 ) .

Notes.

Pluteus costatus is primarily characterized by its pileus with prominent veins, particularly a distinctive pronounced middle vein, and cheilocystidia with mucronate apices.

This species shares morphological similarities with P. ornatus and P. umbrosus , but detailed comparative analyses reveal several distinguishing features. P. costatus is differentiated from P. ornatus by its unstriped pileus margins, smaller basidiospores (avL × avW = 6.2–6.5 × 5.2–5.5 µm), substrate preference for decaying gymnosperm wood ( Pinus ), and distribution in East Asia. In contrast, P. ornatus exhibits striate pileus margins, larger basidiospores (avL × avW = 7.7 × 6.3 µm), preference for decaying angiosperm wood (associated with Fagaceae , Dilleniaceae , Theaceae , with the significant presence of bamboos, Calamus , and Rubus ), and distribution in Vietnam. This distinction is further supported by an ITS genetic distance of 0.029 (SE = 0.007) between these taxa ( Malysheva et al. 2023).

Phylogenetically, our analyses demonstrate that the two specimens of P. costatus form a well-supported monophyletic branch (MLB = 91, BPP = 1, Fig. 3 ) sister to P. umbrosus and P. granularis . P. costatus can be distinguished from these sister taxa by lamellae edge pigmented: white to light brown in P. costatus , distinctly brown in P. umbrosus , and not pigmented in P. granularis ( Kaygusuz et al. 2019) .

Figures

Figure 3. Phylogenetic tree of the / umbrosus clade and / pantherinus lineage 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 18. Basidiomata features. A – C. Pluteus costatus (A, B. FJAU 66589, C. FJAU 66618). D, E. P. umbrosus (FJAU 66590). F – H. P. umbrosoides (FJAU 66615). I, J. P. granularis (FJAU 66612). A – C. Photos by Di-Zhe Guo. D, E. Photos by Jia-Jun Hu. C, F – H. Photos by Gu Rao. I, J. Photos by Zheng-Xiang Qi. Scale bars: 1 cm.

Figure 19. A. Macroscopic characteristics of Pluteus costatus. B. Basidiospores. C. Caulocystidia. D. Pleurocystidia. E. Pileipellis elements. F. Cheilocystidia. Scale bars: 1 cm (A); 10 µm (B, D, F); 20 µm (C, E).