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

Keerthi, V., Justo, Alfredo & Pradeep, C. K., 2024, Two new species of Pluteus (Pluteaceae) from India based on morphology and ITSbased phylogeny, Phytotaxa 670 (3), pp. 161-174 : 169

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) .

Figures

FIGURE 2. ML tree generated from nrITS dataset of the /cinereofuscus clade. Bootstrap values (˃70 %) are shown on or below the branches. New species are indicated in bold. Pluteus phlebophorus and P. eugraptus are used as the outgroup. The root length has been reduced to facilitate graphical representation.

FIGURE 6. Pluteus chimminiensis [TBGT(M) 19318, holotype]. A. Habit in situ; B. Lamella view; C. Basidia; D. Basidiospores; E. Cheilocystidia. Scale bars: A, B= 10 mm; C, D= 10 µm; E= 20 µm. Photos by: V. Keerthi.

FIGURE 7. Pluteus chimminiensis [TBGT(M) 19318, holotype]. A–D. Pleurocystidia; E. Pileipellis; F. Pileal cells; G, H. Caulocystidia. Scale bars: A–D= 10 µm; E–H= 50 µm. Photos by: V. Keerthi.