Pluteus chandrasrikuliae Wannathes, J. Kumla & N. Suwannarach
Pileus 35–40 mm diam., plano-convex to applanate, surface dull, dry, disc hirsute, with tiny fibrillose scales, furfuraceous to subglabrous elsewhere, striate at margin; disc dark brown (6F5-6), margin light brown (5D5-6) or paler. Context thin, soft, greyish white. Lamellae free, close, with 2 series of lamellulae, broad (2–4 mm), greyish orange (5B4-5). Stipe 65–80 × 2.5–3 mm cylindrical, central, fistulose, surface dull, dry, glabrous with a few silky fibrils, white overall. Basidiospores 6–7(–8) × 4–6 µm(x = 6.54±0.58 × 5.29±0.51,Q= 1.17–1.33, q = 1.24 ± 0.06, s = 2) subglobose to broadly ellipsoid, smooth, hyaline, inamyloid, thick-walled. Basidia 12–17 × 6–8 µm, clavate to cylindrical, thin-walled, unclamped. Lamellar edge sterile. Cheilocystidia and Pleurocystidia similar, common on the sides and edges of lamellae composed of two types of cells: (a) irregular shaped cells, often branched, diverticulate with multiple bifurcations 11–32 × 7–18 µm, hyaline to pale yellow, inamyloid, thin- to thickwalled; (b) lageniform to broadly lageniform, 46–58 × 12–20 µm, hyaline, inamyloid, thin-walled to thick-walled (up to 1.5 µm). Pileipellis a cutis composed of parallel cylindrical hyphae 10–14 µm diam., repent, hyaline or with pale brown cytoplasmic pigments, non-incrusted, non-gelatinous; terminal cells over disc clustered, erect, elsewhere repent to suberect, 15–110 × 4–8 µm, narrowly fusoid, acute, with pale brown cytoplasmic pigment, sometimes with some encrusting pigment at apex, thick-walled (up to 1.5 µm). Pileus trama regular, hyphae 2–7 µm diam., cylindrical, hyaline, inamyloid, non-gelatinous, thin-walled. Lamellar trama convergent, hyphae 3–6 µm diam., cylindrical, hyaline, inamyloid, nongelatinous, thin-walled. Stipitipellis a cutis of repent hyphae 4–15 µm diam., cylindrical, hyaline, inamylid, non-incrusted, non-gelatinous, thin-walled. Caulocystidia absent. Clamp connections absent in the examined tissues.
Habit, habitat, and known distribution: Solitary on decaying wood in bamboo thickets, deciduous dipterocarp-oak forests in Thailand.
Additional specimen examined: THAILAND, Phitsanulok Province, Pibulsongkram Ratjabhat University, herbal garden beside Faculty of Science and Technology, on decaying wood, September, 2020, NW 1565.
GenBank accession numbers: holotype (BKF 10214) ITS: MN492649, nrLSU: OM250115; additional specimen (NW 1565) ITS: OM257409, nrLSU: OM250229.
Notes: Pluteus chandrasrikuliae is characterized by a relatively large appearance with applanate pileus, a dark brown scaly disc, white stipe, subglobose to broadly ellipsoid basidiospores with mean dimensions of 6.5 × 5.3 µm and two types of hymenial cystidia as follows: (1) irregular, diverticulate cells and (2) lageniform cells, a cutis-type pileipellis with fusoid-acute, brown terminal cells, lacking caulocystidia and a clamp connection.
According to our phylogenetic analyses inferred from ITS sequences, P. chandrasrikuliae formed a distinct clade as a sister group of several taxa in the ephebeus clade. The remarkable characteristics of P. chandrasrikuliae are as follows: irregular, diverticulate hymenial cystidia indicating phylogenetic distance among Pluteus in sect. Celluloderma. Notably, the irregular, diverticulate cystidia are unusual and rare characteristics that are found in the genus.
Morphologically, P. chandrasrikul is most similar to P. hirtellus and P. riberaltensis due to its macroscopic features, a cutis to trichoderm pileipellis with long, acute, brown terminal cells and the absence of caulocystidia. However, P. hirtellus differs by appearing globose to subglubose (avQ = 1.7), having slightly smaller basidiospores with mean dimensions of 5.3 × 4.96 µm, and the absence of irregular, diverticulate hymenial cystidia. Pluteus riberaltensis differs by forming globose (avQ = 1.08) basidiospores and is absent of irregular, diverticulate hymenial cystidia. Based on certain macroscopic features, such as a dark brown to brown pileus and white stipe, P. chandrasrikul is close to P. ephebeus, P. hispidulus var. cephalocystis, P. escharites, and P. albostipitatus. Pluteus ephebeus forms larger basidiomata with a pileus of 35–70 mm in diam., and a stipe that is 45–95 × 4–8 mm and covered with brown fibrils. It is utriform to fusiform or lageniform hymenial cytidia but lacks diverticulate cystidia. Pluteus hispidulus var. cephalocystis forms smaller basidiomata with a pileus of 7–23 mm in diam., a stipe of 17–40 × 1–3 mm, a conical to applanateumbonate pileus, and the absence of pleurocystidia. Pluteus escharites differs from the new species by forming smaller basidiospores (5–6 × 4.5–5 µm). It is versiculose with ellipsoid to pyriform cheilocystidia and lacks pleurocystidia. Pluteus albostipitatus forms larger basidiospores (7.5–10 × 6.2–7.5 µm). It is ventricose with a rounded to subcapitate apex, thin- to relatively thick-walled pleurocystidia, and clavate with thin walled cheilocystidia. The new species is somewhat close to P. atrofusens in terms of its cutis pileipellis, its spore size, and the fact that it has thin- to thick-wall hymenial cysdidia without hooks. However, it differs from the latter in terms of the shape of the cystidia, a smaller basidiomata with a pileus of 17–23 mm in diam, a stipe of 45–51 mm long, and the presence of cualocystidia.