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

Pluteus fuscipruinatus V. Keerthi & C.K. Pradeep, sp.nov. (Figs. 3–5) MycoBank: MB854542 Diagnosis:—This species is characterized by a brownish pruinose pileus and stipe, polymorphic cheilocystidia, small globose to subglobose basidiospores and a trichoderm type of pileipellis in contrast to a cutis type in most other species of the /ephebeus clade. Holotype:— India, Kerala State, Thiruvananthapuram district, Palode, JNTBGRI campus: 8.75°N, 77.02°E, elev. 150 m, 19 September 2023, Keerthi TBGT(M)19392! GenBank [ITS]: PP938400 Etymology:— fuscipruinatus, refers to the brown pruinose pileus of the new species Description:— Pileus 12−40 mm in diam., plano-convex to applanate with a small broad obtuse umbo or with a shallow depression; surface brownish orange to brown (6C3/6E4/6E5) with dark brown (6F6−6F4) disc, pruinose throughout when young, most densely at the disc, later on with less pruina, except at the disc which remains densely pruinose, striate near pileus margin, dry, non-hygrophanous; margin straight, entire to incised. Lamellae free, orange-white to dull red with age (5A2/6A2/6A3/7A2/7A4/7B2/8B3), up to 5 mm wide, crowded with lamellulae of different lengths; edge concolorous with the sides, entire. Stipe 20−48 × 1−5 mm, central, cylindric, curved, brittle in some, equal or tapering upwards from a slightly broad base, solid to hollow; surface white with dark brown (6E5/7E5/7F5/8F8) minute pruina throughout, dense at the extreme base, smooth to glabrous at the extreme apex. Pileus context up to 1.5 mm thick, white, thin, soft. Mycelial mat present at the extreme base. Odor none. Taste not recorded. Basidiospores 4.2–5.2 × 4.1–5.1 µm (avL= 4.84 ± 0.26 µm, avW=4.5 ± 0.22 µm); Q = 1.0–1.15, Qm= 1.07, globose to subglobose, hyaline, smooth, thick-walled. Basidia 14.7−27.7 × 6.3−8.6 µm, clavate to cylindro-clavate, 4-spored, smooth, thin-walled, hyaline. Lamella edge sterile with crowded cheilocystidia. Cheilocystidia 10.4–98.6 × 5.5–16.5 µm, polymorphic, broadly clavate, fusiform, utriform to lageniform with obtuse to subobtuse with a long narrow apex, thin-walled, hyaline. Pleurocystidia moderately abundant, 47.1–82.2 × 16.3–24.7 µm, fusiform, utriform to lageniform with obtuse apex, thin-walled, hyaline. Pileipellis a trichoderm composed of polymorphic elements, 85.8−93.7 × 14.0−39.9 µm, narrowly clavate, cylindro-clavate, lageniform to fusiform, thin-walled with brown intracellular contents. Stipitipellis a cutis composed of parallel hyphae, 3.6–23.2 µm wide, thin-walled, hyaline. Caulocystidia abundant, present throughout the surface of the stipe, 24.5−79.3 × 7.8−22.9 µm, polymorphic, clavate, cylindro-clavate to fusiform with round to subobtuse apex, thin-walled with brown intracellular contents. Clamp connections absent. Habitat and phenology:—Solitary to scattered on soil or dead decaying angiosperm twig. June−September. Additional specimens examined:— INDIA. Kerala State, Thiruvananthapuram district, Palode, JNTBGRI campus: 8.75°N, 77.02°E, elev. 150 m, 08 June 2023, Keerthi TBGT(M)19189; ibid., 19 June 2023, Keerthi TBGT(M)19219; ibid., 16 July 2023 Keerthi TBGT(M)19323; ibid., 14 September 2023, Keerthi TBGT(M)19385; ibid., 14 September 2023, Keerthi TBGT(M)19386; ibid., 19 September 2023, Keerthi TBGT(M)19393. Notes:—Phylogenetic analyses with nrITS sequence data (611 bp), place Pluteus fuscipruinatus in the ephebeus clade of Pluteus sect. Celluloderma. Two Pluteus sequences (KR002882; KR002899) from India exhibit 98 % sequence similarity with the current species. However, morphological details of the collections of these sequences are lacking, so they cannot be compared to our species. Molecularly, the closest (named) relatives of P. fuscipruinatus are P. hirtellus and P. squarrosus. Sequence comparison reveals 97 % sequence similarity with 14 nucleotide differences with P. hirtellus (MG968804) from Sáo Tomé. Morphologically, P. hirtellus differs by its slightly smaller, shaggy, fibrillose, grayish brown pileus (23–35 mm), smaller globose to subglobose basidiospores (4.5–6 × 4.2–5.5 µm), smaller clavate hymenial cystidia, epithelial pileipellis, and the absence of caulocystidia (Desjardin & Perry 2018). Pluteus squarrosus (NR169965) from China, differs at 15 nucleotide positions and morphologically by its comparatively smaller, brown, squarrose to verrucose, squamulose (18–35 mm) pileus, larger basidiospores (5.5–6.5 × 5–6 µm), smaller cheilocystidia (35–42 × 9–18 µm), clavate pleurocystidia, and smaller fusoid to lageniform caulocystidia (Hosen et al. 2019). Other species with notable morphological similarities particularly the dark brown pileus include the following species described from Sri Lanka: P. psichiophorus (Berk. & Broome) Sacc. (1887: 670), P. stigmatophorus (Berk. & Broome) Sacc. (1887: 674), P. brunneopictus (Berk. & Broome) Sacc. (1887: 669), P. albolineatus (Berk. & Broome) Sacc. (1887: 671), and P. fusconigricans (Berk. & Broome) Sacc. (1887: 673). Pluteus psichiophorus is distinguished by its diminutive (0.7–20 mm), fibrillose-squamulose, rimose pileus, glabrous stipe, larger ovoid basidiospores (6–8 × 5–6.5 µm), smaller hymenial cystidia, and a disrupted epithelial pileipellis (Pegler 1986). Pluteus stigmatophorus is characterized and distinct by its larger, squamulose, radially striate pileus, dark brown lamellar edges, clavate hymenial cystidia, and epithelial pileipellis intermixed with elongate dermatocystidia (Pegler 1986). Brownish, rimose, radially fibrillose-striate pileus, glabrous stipe, larger ovoid basidiospores (7–9 × 5–6 µm), smaller pyriform to ellipsoid cheilocystidia with brown contents, and smaller ellipso-pedicellate pleurocystidia (26–44 × 15–20 µm) distinguish P. brunneopictus (Pegler 1986).A cracked pileus, glabrous stipe, larger broadly ovoid basidiospores (5–6.5 × 4.5–5.5 µm), smaller inflated pyriform cheilocystidia, vesiculose to broadly cylindrical pleurocystidia, and a disrupted epithelial pileipellis separate P. albolineatus from the present taxon (Pegler 1986). Pluteus fusconigricans is distinguished by its smaller (10–25 mm), radially striate pileus, dotted brownish lamella edges, glabrous stipe, larger ovoid basidiospores (5.5–7 × 4.2–5.2 µm), smaller pigmented hymenial cystidia, and an epithelial pileipellis (Pegler 1986). Some of the Indian species in P. sect. Celluloderma, must be compared such as P. delicatulus C.K. Pradeep & K.B. Vrinda (2006: 95), P. brunneosquamulosus C.K. Pradeep & K.B. Vrinda (2012: 870), P. fuscopunctatus C.K. Pradeep & V. Keerthi (2023: 2), P. parvulus Keerthi, Ševčíková & C.K. Pradeep (2024: 115), and P. pauxillus Keerthi & C.K. Pradeep (2024: 120). The very small, thin, delicate, fragile basidiomata, small pileus (7–10 mm), globose basidiospores, smaller clavate hymenial cystidia, epithelial pileipellis, and absence of caulocystidia separate P. delicatulus from the new species (Pradeep & Vrinda 2006). Pluteus brunneosquamulosus is distinct by its smaller (8–26 mm), rimose pileus, larger subglobose to broadly ellipsoid basidiospores (4.5–7 × 4.5–6 µm), smaller lageniform hymenial cystidia, and hymeniderm pileipellis (Pradeep et al. 2012). Larger basidiomata (22–60 mm), large basidiospores (5.6–6.0 × 5.2–6.0 µm), large cheilocystidia (30.0–159.9 × 11.4–32.5 µm), and lageniform pleurocystidia characterize P. fuscopunctatus (Keerthi & Pradeep 2023). A small, depressed pileus (3.5–22 mm), globose to ellipsoid basidiospores, and smaller hymenial cystidia separate P. parvulus while P. pauxillus is distinct by its smaller (10–17 mm), shallow, depressed pileus, broadly ellipsoid to ellipsoid basidiospores, smaller hymenial cystidia, and a mixed epithelial type pileipellis (Keerthi et al. 2024).

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