Pleurotus placentodes (Berk.) Sacc., Syll.

Liu, Xiao-Bin, Li, Jing, Horak, Egon & Yang, Zhu L., 2016, Pleurotus placentodes, originally described from Sikkim, rediscovered after 164 years, Phytotaxa 267 (2), pp. 137-145 : 142-143

Pleurotus placentodes (Berk.) Sacc., Syll. fung. (Abellini) 5: 359 (1887) Figs. 2–3

Basionym: Agaricus placentodes Berk. , Hooker’s J. Bot. Kew Gard. Misc. 4: 104 (1852).

Synonym: Dendrosarcus placentodes (Berk.) Kuntze. Rev. Gen. Plant. 3: 464 (1898).

Description:— Basidiome medium-sized. Pileus flabelliform to orbiculate, occasionally obovate, 40–70 mm from point of attachment to margin, 40–80 mm in diam.; surface pale ochre, greyish brown to brownish grey (2A2, 3B2–3), becoming ochre to biscuit-colored (6E6–8) in dry conditions, glabrous, smooth, faintly innately streaked towards margin, slightly viscid when wet, finely cracked when dry; margin paler colored, inrolled when young, becoming straight at maturity; context white (1A1), unchanging, relatively thin (up to 8 mm wide near base). Lamellae decurrent, crowded to subdistant, narrow (up to 3 mm wide), white (1A1), occasionally branched or anastomosing; lamellar edges entire and concolorous; lamellulae 2–3 tiers. Stipe lateral, 5–10 × 5–8 mm, subcylindric, whitish to greyish (1A1, 3B3, 4B3). Odor pleasant, orange-like or indistinct; taste mild. Spore print white to cream-colored (1A1, 3A2).

Basidiospores [100/4/4] (5.5) 6–8 (9) × (3.5)4–5 μm, Q = (1.35–) 1.45–1.75 (–1.80) (Q = 1.58 ± 0.10), ellipsoid to subovoid, sometimes elongate, colorless and hyaline, thin-walled, smooth, inamyloid, non-dextrinoid. Basidia 25–30 × 6.5–7.5 μm, narrowly clavate to clavate, thin-walled, 4-spored; sterigmata 3–4 μm long. Cheilocystidia 15–20 × 3–7 μm, not well-differentiated, clavate to broadly clavate, sometimes nearly cylindrical, occasionally mucronate, colorless and hyaline, thin-walled. Pleurocystidia absent. Lamellar trama monomitic, composed of subregularly to irregularly arranged thin- to thick-walled (up to 1 μm diam.), colorless and hyaline, branching, filamentous hyphae 2–8(12) μm wide; terminal cells 50–100 μm long, non-skeletalized. Subhymenium composed of frequently branching hyphae, 3–5 μm wide. Pileipellis a 20–50 μm thick cutis composed of repent, radially arranged, yellowish to brownish, thin- to slightly thick-walled (up to 0.5 μm diam.) filamentous hyphae, 3–6(8) μm wide; suprapileipellis slightly gelatinized, often with coralloid to finger-like hyphal tips, 5–20 × 2–4 μm. Pileitrama monomitic, composed of radially to irregularly arranged thin- to slightly thick-walled (up to 1 μm diam.), colorless and hyaline, filamentous hyphae, 3–15 μm wide. Stipititrama composed of more or less irregularly arranged, frequently branching and septate, slightly thick-walled (0.5–1.5 μm diam.), colorless and hyaline monomitic hyphae, 3–12 μm wide. Clamp connections abundant at all septa.

Habitat and known distribution:—Growing on decaying wood of Betula (reported to be the host substrate of the type material) and Picea in subalpine forests dominated by Abies , Betula , Picea and Rhododendron ; during summer (June to September) at 3000–4200 m elev., in southwestern China. Originally described from Sikkim, India.

Specimens of Pleurotus placentodes examined: INDIA. Sikkim, on Betula wood, 3353 m elev., 1849, Hooker f. 16 (K, holotype). CHINA. Yunnan Province, Yulong County, Shitou, 3000 m elev., 5 September 2009, G. Wu 249 (HKAS 57781); Dali City, locality unknown, Y.C. Zhao (HKAS 94408 and 94409, dried strains); Tibet Autonomous Region, Linzhi County, Sejilashan, 4200 m elev., on Betula sp. , 29 Jun. 2009, B. Feng 416 (HKAS 57145, epitype designated here); same locality, 4100 m elev., 6 August 2010, WSX 2010806 (HKAS 94410).

Specimens of Pleurotus djamor examined: SRI LANKA. Kandy, Mt. Hanthana, 11 IX 2011, S. C. Karunarathna SK-76 ( HKAS 94069 ) ; Knuckels Range , 16 IX 2011, S. C. Karunarathna SK-83 ( HKAS 94070 ) .

Figures

FIGURE 2. Basidiomes of Pleurotus placentodes in situ. a. HKAS 57781; b. HKAS 57145. Bars = 2 cm Photos by B. Feng and G. Wu.

FIGURE 3. Microscopic characters of Pleurotus placentodes. a. Basidia at different stages of development and subhymenium elements (HKAS 57781); b. Basidiospores (HKAS 57781); c. Broadly clavate to subcylindrical cheilocystidia (HKAS 57781); d. Mucronate cheilocystidia (HKAS 94410); e. Pileipellis (HKAS 57781); f. Basidiospores (HKAS 57145); g. Mediostratum of lamellar trama (HKAS 57781). Bars 1, 3, 4, 5 and 7 = 20 μm, 2 and 6 = 10 μm. Drawings by Zhu L. Yang.