Pluteus griseodiscus Jiang Xu & T.H. Li, 2015

Xu, Jiang, Li, Tai Hui, Justo, Alfredo & Ge, Zai Wei, 2015, Two new species of Pluteus (Agaricales, Pluteaceae) from China, Phytotaxa 233 (1), pp. 61-68 : 62-65

Pluteus griseodiscus Jiang Xu & T.H. Li , sp. nov. Fig. 2 a–c , Fig. 3

MycoBank: MB 812366; Fungal Name: FN570175.

Diagnosis:— Differing from Pluteus atromarginatus in having paler pileus, concolorous lamellar edges, thick-walled cheilocystidia, and abundant caulocystidia.

Type:— CHINA, Guangdong Province, Guangzhou City, Tianlu Lake Forest Park, elev. 268 m, at 113°25.058'E, 23°13.383'N, 29 May 2013, Jiang Xu, M. Zhang & S. H. Zhou, GDGM42280 (Holotype; nrITS KR350490 ) .

Etymology:— the epithet griseodiscus is from the Latin words “ griseus ” (gray) and “ discus ” (umbo), making reference to the grayish umbo of the pileus.

Pileus 65–76 mm in diam. campanulate when young, becoming plano-convex to applanate with a low and broad umbo at the center; surface glabrous or with some innately fibrils at center or around, dry or viscid when moist, whitish to brownish gray (6C2), with some pinkish tints when mature; margin exceeding lamellae and short translucently striate. Lamellae free, moderately crowded, thin, ventricose, up to 13 mm wide, white to pinkish; about (9–10) complete lamellae per cm at pileus margin, with 2–3 lamellulae between two lamellae; edge entire, concolourous. Stipe 80–90 × 5–6 mm, central, equal or slightly enlarged towards base, occasionally curved, white or paler in mature basidiomata, solid, longitudinally striate and covered by whitish fibrils, with white mycelium at base. Context white, unchanging. Odor not distinctive. Taste not recorded.

Basidiospores [90/3/3] 6.0–8.0(–10.0) × (4.0–)5.0–6.0(–7.0) μm, avl × avw=7.5 × 5.5 μm, Q=1.17–1.80, avQ= 1.42, broadly ellipsoid to elongate, smooth, thick-walled. Basidia 26–37 × 6–10 μm, clavate, 4-spored, thin-walled. Pleurocystidia abundant, 65–115 × 12–27 μm, metuloid, (narrowly) fusiform or lageniform, with 2–4 hooks at apex, thick-walled (2–5 μm thick at neck), colorless. Intermediate cystidia rare, with a sharp transition between pleurocystidia and cheilocystidia. Lamellar edge sterile. Cheilocysidia abundant, 47–72 × 9–12 μm, fusiform or bifurcate, strongly tapering towards apex, thick-walled, colorless or with brown intracellular pigment. Hymenophoral trama made up of non-septate hyphae in 9–12 μm diam., convergent, thin-walled, hyaline. Pileipellis a cutis of cylindrical hyphae; terminal elements 75–100 × 8.5–15 μm, strongly tapering towards apex, with brown intracellular pigment, thin-walled. Stipitipellis a cutis of hyphae 6–10 μm wide, hyaline or with brown intracellular pigment, thin-walled. Caulocystidia abundant, present over the whole stipe surface, 40–90 × 7–14 μm, cylindrical to sub-fusiform with acute apex, thin walled, hyaline. Clamp connections common, especially in pileipellis hyphae.

Habit, habitat and distribution:— Solitary. A total of four basidiomata was collected on the rotten wood of broad-leaved trees (e.g. Castanopsis sp. , Quercus sp. ) between mid-May and mid-July in a forest park at elve. 250– 300 m. Asia: Known only from southern China.

Additional specimens examined:— China, Guangdong Province: Guangzhou city, Tianlu Lake Forest Park, in broad-leaved forests,at 113°25.060'E, 23°13.385'N,elev. 270m, 6July2013, Jiang Xu ( GDGM42284 ;nrITS KR350491 ) ; ibid., 3 July 2014, Jiang Xu ( GDGM42373 ; nrITS KR350492 ) ; ibid., 3 July 2014, Jiang Xu ( GDGM42377 )

Discussion:— The combination of whitish to pale greyish pileus, habitat on angiosperm wood, thick-walled cheilocystidia and abundant caulocystidia are diagnostic for P. griseodiscus .

Although P. griseodiscus is placed with high support (100% BS, Fig. 1 ) in the atromarginatus clade, its paler pileus and the habitat on broadleaf wood are quite distinctive. All known taxa in this clade have darker colors of the basidiomata, pigmented lamella edges, thin-walled cheilocystidia, and habitat on coniferous wood ( Justo et al. 2014).

Other taxa in Pluteus section Pluteus that have white or paler basidiocarps are also morphologically distinguished easily from the new species: P. hongoi Singer (1989: 95) , as well as its synonyms P. albineus Bonnard (2001: 131) and P. nothopellitus Justo & M.L. Castro (2007b: 222) , differs in the lack of clamp-connections and mainly in the thin-walled cheilocystidia ( Justo et al. 2014); P. orestes Vellinga & Justo ( Justo et al. 2014: 41) has relatively larger basidiospores (9.0–9.9 × 6.0–7.3 μm), narrow cylindrical thin-walled cheilocystidia, and habitat exclusively on coniferous wood in mountainous areas in Western North America; P. pellitus (Pers.: Fr.) P. Kumm. (1871: 98), known only from Western Europe, has smaller basidiospores (5.8–6.5 × 4.3–4.6 μm), thin-walled cheilocystidia and no caulocystidia ( Justo et al. 2014); while P. petasatus (Fr.) Gillet (1876: 395) and P. leucoborealis Justo, E.F. Malysheva, Bulyonkova & Minnis ( Justo et al. 2014: 58), though morphologically similar, lack clamp-connections and caulocystidia, and have thin-walled cheilocystidia ( Justo et al. 2014).

The presence of thick-walled cheilocystidia is though unusual in section Pluteus , a few species with this invite comparison with the new species: P. amphicystis Singer (1959: 213) , known from Bolivia ( Singer 1959), Martinique ( Pegler 1983), India ( Pradeep et al. 2002) and Mexico ( Rodríguez & Guzmán-Dávalos 1997), can be separated by its yellow pileus, pleurocystidia without apical hooks, and lack of clamp-connections. Another species known from the Americas is P. spinulosus Murrill (1917: 138) , but it differs from P. griseodiscus in the brown pileus, the pleurocystidia mostly without apical hooks and common in lateral ornamentation, and in the absence of caulocystidia; in addition, although P. spinulous was described having exclusively thick-walled cheilocystidia ( Pegler 1983), the observation on the type collection at NY (A. Justo, pers. obs.) has revealed that the lamellar edge is mostly composed of a continuous strip of thin-walled cheilocystidia, and along that strip some metuloid cystidia do occur. A modern collection of P. spinulosus from Bolivia appears in the phylogeny as sister to the atromarginatus clade ( Fig. 1 ). The Asian species Pluteus horridilamellus S. Ito & S. Imai (1940: 46) has thick-walled and fusiform-lageniform pleurocystidia, cheilocystidia without apical or lateral hooks, even thick-walled pileocystidia and caulocystidia, and pileipellis without clamp-connections, which are different from those of P. griseodiscus ( Kobayashi 2002) .

Figures

FIGURE 1. Best tree from the ML analysis of the nrITS dataset of selected Pluteus sect. Pluteus species. Support values are given on or below the branches.

FIGURE 2. a–c.Basidiomata of P.griseodiscus (b, c. GDGM42280, d. GDGM42377).d.Basidiomata of P.purpureofuscus (HKAS48956– holotype, photo by Z.W. Ge.). Scale bars: a, b, c, d = 1 cm.

FIGURE 3. Pluteus griseodiscus (GDGM42280–holotype). a. Basidiospores. b. Basidia. c. Caulocystidia. d. Cheilocystidia. e. Pleurocystidia. f. Pileipellis elements. Scale bars: a, b, d = 10 μm; c, e, f = 20 μm.