Pluteus chimminiensis V. Keerthi & C. K. Pradeep 2024, sp.nov.

Pluteus chimminiensis V. Keerthi & C.K. Pradeep sp.nov. (Figs. 6, 7) MycoBank: MB854545 Diagnosis:—Differs from the closely related P. multiformis by its dark brown pruinose pileus, smaller broadly ellipsoid basidiospores, polymorphic pleurocystidia and molecularly by 38 nucleotides in a pairwise comparison. Holotype:— INDIA. Kerala State: Thrissur district, Chimmini wildlife sanctuary: 10.43°N, 76.46°E, elev. 87 m, 16 July 2023, Keerthi TBGT (M)19318! GenBank [ITS]: PP938401. Etymology:— chimminiensis refers to the type locality of this species Description:— Basidiomata small to medium. Pileus 4–35 mm in diam., applanate, convex to plano-convex with a shallow depression or with small obtuse umbo at centre; surface chocolate brown to dark brown (6F4/6F5/8F4/8F5) with minute pruina, often breaking open to appear subsquamulose in dry weather, pruina denser at the disc, dry, non-hygrophanous; margin straight, entire, incised in some. Lamellae free, orange-white (5A2/6A2), up to 2 mm wide, crowded with lamellulae of different lengths; edge concolorous to the sides, entire. Stipe 7.5–20 × 1.5–3 mm, central, cylindric, curved, hollow, equal or tapering upwards from a broad base; surface white in the upper 1/3, grayish below, brown pruinose throughout, dense at the extreme base. Context in pileus up to 1 mm thick, white, thin, soft. Odor none. Taste not recorded. Basidiospores 5.1–5.8 × 4.1–4.8 µm (avL= 5.40 ± 0.19 µm, avW= 4.3 ± 0.21µm); Q = 1.16–1.30, Qm= 1.22, broadly ellipsoid, hyaline, smooth, thick-walled. Basidia 14.7−32.9 × 7.4−12.0 µm, cylindro-clavate, 4-spored, smooth, thin-walled, hyaline. Lamella edge heteromorphic with crowded cheilocystidia. Cheilocystidia 22–39 × 11–22 µm, mostly clavate, cylindro-clavate, and fusiform, thin-walled, hyaline or with brown intracellular contents. Pleurocystidia scattered, polymorphic, 38.6−66.3 × 9.0–19.0 µm, fusiform, lageniform to utriform, thin-walled, hyaline. Pileipellis an epithelium consisting of vesiculose -clavate, pedunculate, globose to subglobose cells, 21.9−54.9 × 15.0−48.7 µm, thin-walled with brown intracellular contents. Stipitipellis composed of parallel hyphae, 3.3–42.0 µm wide, thin-walled, hyaline. Caulocystidia present, scattered throughout the stipe surface, abundant, dense at the extreme base, 25.6−51.5 × 13.5−21.4 µm, clavate, vesiculose-clavate, cylindro-clavate, thin-walled with brown intracellular contents. Clamp connections absent. Habitat and phenology:—Scattered on dead decaying angiosperm tree log in tropical evergreen forest. Kerala State, India. July. Additional specimens examined:— Thrissur district, Chimmini wildlife sanctuary: 10.43°N, 76.46°E, elev. 87 m, 16 July 2023, Keerthi TBGT(M)19314; ibid., 16 July 2023 Keerthi TBGT(M)19315; ibid, 16 July 2023 Keerthi TBGT(M)19324. Notes:—Molecular analysis indicates the close affinity of Pluteus chimminiensis with the species in the cinereofuscus clade. BLAST search revealed the closest relatives to be a cluster of undescribed Pluteus species (Fig. 2). Pluteus multiformis Justo, A. Caball. & G. Muñoz (2010: 647) from Spain shows 92 % sequence similarity however, is distinct in morphology by its small rugose-venose, translucently striate pileus (15−20 mm), dark-edged lamella, larger globose, or sub-globose basidiospores (6−8 × 5−7.5 µm), larger fusiform to lageniform pleurocystidia (40−71 × 10−20 µm), and larger (35−65 × 10−15 µm), clavate, non-hyaline cheilocystidia (Justo et al. 2011c). Pluteus chimminiensis exhibits morphological similarities to certain Sri Lankan and East African species having a brownish pileus, such as P. fusconigricans (Berk. & Broome) Sacc. (1887: 673) and P. pulverulentus Murrill (1917: 137). However, the former stands out morphologically by its relatively smaller pileus (5−20 mm), larger basidiospores (5.7−7.5 × 4.5−6 μm), smaller non-hyaline cheilocystidia (27−35 × 10−18 μm), a hymeniform pileipellis, and the absence of caulocystidia (Pegler 1986). The latter species is distinct with its comparatively smaller pileus (10−20 mm), larger globose basidiospores (4.7−6.5 × 4.3−6.3 μm) and smaller hymenial cystidia (Pegler 1977). Some recently described Pluteus species with morphological resemblance to the new species includes P.absconditus Justo, Kalichman & S.D. Russell (2023: 22), P. cutefractus Ferisin, Dovana & Justo (2023: 25), P. fuscodiscus Ferisin, E.F. Malysheva, Ševčíková, Kaygusuz, Heilm. Claus. & I. Saar (2023: 27), P. anatolicus Kaygusuz, Knudsen, Menolli & Turkekul (2021: 243), and P. keselakii Ševčíková, P.A. Moreau & Borovicka (2020: 184). Pluteus absconditus originally described from USA (Ševčíková et al. 2023) differs by its relatively larger granulose-squamulose pileus (15−40 mm), larger basidiospores (5.0−6.8 × 4.3−5.8 μm), larger cheilocystidia (22−42 × 11−22 μm), and a hymeniderm pileipellis with fusiform to cylindrical elements. Pluteus cutefractus, a Slovenian species stands out with its smaller venose pileus (10−29 mm), larger, ovoid hymenial cystidia, and a hymeniderm pileipellis with utriform to fusiform elements (Ferisin et al. 2020). A small, granulose-pruinose pileus, smaller basidiospores (4.8−6.5 × 4.0−5.5 μm), absence of pleurocystidia, and a pileipellis with fusiform elements differentiate P. fuscodiscus (Ševčíková et al. 2023). Pluteus anatolicus is distinguished by its small, cracked pileus, larger basidiospores (5.0−6.8 × 4.3−5.8 μm), larger cheilocystidia (16.5−53 × 8.0−22.5 μm), and absence of caulocystidia (Kaygusuz et al. 2021). A small (15−27 mm), rugose-venose pileus, larger hymenial cystidia, and larger basidiospores (6−8 × 6−7 μm) distinguish P. keselakii (Ševčíková et al. 2020).

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