Nigroboletus roseonigrescens Gelardi, Vizzini, E. Horak, T.H. Li & Ming Zhang, in Gelardi et al., PLoS ONE 10(8): e0134295, 6 (2015)
Etymology: the specific epithets “roseo” (pink) and “nigrescens” (blackening) are derived from Latin and refer to the pinkish color of pileus and stipe which turn blackish when damaged.
Basidiomes small to medium sized. Pileus (3.0–) 3.2–8.0 (–10.0) cm broad, at first hemispherical then persistently convex and finally broadly pulvinate-flattened, moderately fleshy, firm at the beginning but progressively softer with age; margin steady to faintly wavy-lobed, initially involute then curved downwards and eventually plane or even uplifted, not or only a little extending beyond the tubes; surface matt, dry, very finely tomentose in the early stage of development but later smooth and glabrous, not cracked; cuticle evenly pink or pastel rose (Flesh Pink, Chatenay Pink, Venetian Pink, Coral Pink,), slowly staining grayish (Pale Mouse Gray, Pale Quaker Drab) to dull sooty brown (Raw Umber, Blackish Brown) and finally blackening (Sooty Black) on handling, when injured or even at the slightest contact with rain drops; subcuticular layer pale cream. Tubes at first thin then broader and always shorter than the thickness of the pileus context, particularly in young specimens (up to 1 cm long), adnate to subdecurrent on stipe, straw yellow (Martius Yellow) to bright yellow (Lemon Yellow) and finally olive yellow (Javel Green), bruising dark gray (Deep Mouse Gray, Quaker Drab) to blackish (Sooty Black) when cut. Pores initially concave or even, later with a convex–anticlinal surface, small at first then gradually wider (up to 1.5 mm diam), simple, roundish to angular and radially arranged, concolorous with tubes, turning dark grayish (Deep Mouse Gray, Quaker Drab) and quickly becoming blackish (Sooty Black) when bruised. Stipe (2.0–) 3.2–6.0 (–7.0) × (0.8–) 1.0–1.7 (–2.0) cm, shorter than or more often as long as the pileus diameter at maturity, central to slightly off–center, solid, firm, dry, straight or curved, cylindrical or fusiform to more frequently swollen towards the base, sometimes squashed, ending with a roundish base, not rooting; surface devoid of reticulum, smooth at apex but finely pruinose–punctate elsewhere, evelate; at first uniformly straw yellow (Martius Yellow) to bright yellow (Lemon Yellow), later pinkish (Flesh Pink, Chatenay Pink, Venetian Pink) to pale orange-yellow (Orange), quickly turning gray-blackish (Blackish Mouse Gray, Sooty Black) when pressed; basal mycelium white (White), rhizomorphs brownish (Sayal Brown). Context firm when young, later soft in the pileus, up to 1.7 cm thick in the central zone, a little more fibrous in the stipe, yellowish (Martius Yellow) to pale cream (Maize Yellow) in the pileus, of a deeper yellow in the stipe but dirty yellowish (Apricot Yellow) and occasionally with orange hues (Ochraceous–Orange) towards the base; evenly but slowly turning pale pinkish (Light Pinkish Cinnamon) on exposure especially in the pileus, then grayish–violaceous (Dark Purple–Drab) and finally becoming blackish (Sooty Black); subhymenophoral layer pale cream (Maize Yellow, Plate IV); dried material sordid blackish (Sooty Black, Plate LI) throughout. Odor faintly fruity, agreeable. Taste mild. Macrochemical reactions: 20% KOH: blackish on pileus, hymenophore and stipe surface, dull ochraceous on context; FeSO4: no reaction.
Basidiospores [157/7/4] (5.2–) 7.4 ± 0.77 (–10.1) × (4.0–) 4.7 ± 0.33 (–6.4) μm, Q = (1.27–) 1.30–2.06 (–2.15), Qm = 1.57 ± 0.15, V = 86 ± 20 μm³, asymmetric, broadly ellipsoid to subovoid, less frequently ellipsoid in side view, broadly ellipsoid to ovoid or even subglobose in face view, smooth, with a short apiculus and without suprahilar depression, adaxially applanate, apex rounded, thin-walled (0.3–0.5 μm), straw yellow coloured in water and 5% KOH, having one large or occasionally two oil droplets when mature, inamyloid to very slighty dextrinoid, acyanophilic and showing an orthochromatic reaction. Basidia 26–44 (–48) × 6–10 (–12) μm (n = 32), cylindrical to cylindrical–clavate, rarely truly clavate, moderately thick–walled (0.5–1.0 μm), predominantly 4–spored but frequently also 1–, 2– or 3–spored, with relatively long sterigmata (2–6 μm), hyaline to very pale yellowish in water and hyaline to yellowish in KOH, usually containing straw-yellow oil guttules, without basal clamps, inamyloid; basidioles cylindrical to clavate, about the same size as basidia. Cheilocystidia 30–59 (–63) × 7–16 (–18) μm (n = 47), frequent, moderately slender, projecting straight to sometimes flexuous, fusiform to ventricose–fusiform or sublageniform, occasionally clavate or mucronate, with short neck and rounded or rarely pointed tip, smooth, moderately thick-walled (0.6–1.2 μm), with a brownish to dark brown plasmatic pigment in water and KOH, occasionally hyaline, reddish-brown (dextrinoid) in Melzer’s, without epiparietal encrustations but sometimes with brownish to dark brown, congophilous plaques. Pleurocystidia 31–66 (–68) × 10–18 μm (n = 29), color, size, shape and chemical reactions as in cheilocystidia, very frequent. Pseudocystidia present but rare, rising from the oleiferous hyphae of the inner hymenium, up to 125 × 12 μm (coll. MG524a). Pileipellis a trichoderm consisting of erect subparallel to loosely interwoven (palisadoderm), filamentous and sinuous, unbranched hyphae usually not constricted at septa, tending to remain erect or to be repent only in the outermost layer, not embedded in gelatinous matter; terminal elements (22–) 31–150 (–156) × 6–15 (–18) μm (n = 36), slender, cylindrical, only rarely short, acorn–shaped or bullet–shaped, occasionally cystidioid, apex rounded–obtuse and enlarged or tapered, moderately thick–walled (0.5–1.0 μm), with a brownish–yellow to dark brown plasmatic pigment in water and KOH and reddish-orange (inamyloid to weakly dextrinoid) in Melzer’s, smooth to more often ornamented with subtle granular or zebra–pattern epiparietal encrustations; subterminal elements similar in shape, color and dimensions with terminal ones. Stipitipellis a texture of slender, subparallel to loosely intermingled and longitudinally running, smooth walled, adpressed hyphae, 2–7 (11) μm wide, some hyaline to pale yellow but others with brownish to dark brown plasmatic pigment in water and KOH; the stipe apex distinctly covered with caulobasidioles, spore-bearing caulobasidia (mainly 4–, 2– and 3–spored but also 1–spored, 29–37 × 8–9 μm (n = 4), sterigmata 3–6 μm long) and very frequent projecting caulocystidia similar in shape, size, color and chemical reactions to the hymenial ones, sporadically with secondary septa, (32) 38–72 (86) × (6) 8–15 (18) μm (n = 16), moderately thick–walled (up to 1.2 μm); elsewhere the stipe surface exhibits a layer of sterile cystidioid elements. Lateral stipe stratum under the caulohymenium present and well differentiated from the stipe trama, of the “boletoid type”, at the stipe apex a 40–100 (160) μm thick layer consisting of divergent, inclined and running towards the external surface, loosely intermingled and sparingly branched hyphae remaining separate from each other and faintly to distinctly embedded in a gelatinous substance; the stratum reducing during development and finally disappearing at maturity. Stipe trama composed of densely arranged, loosely to strongly interwoven, filamentous, smooth hyphae, 4–22 μm broad, some hyaline and inamyloid, others (oleiferous hyphae) with a brownish to dark brown plasmatic pigment in water and KOH and dextrinoid in Melzer’s. Hymenophoral trama bilateral divergent of the “Boletus–type” or less frequently intermediate between the “Boletus–type” and the “Phylloporus–type”, with moderately to distinctly divergent and loosely arranged, gelatinized hyphae, lateral strata hyphae often branched, constricted at septa, in transversal section remaining separate and (1–) 2–8 (–10) μm apart, some hyaline to very pale yellowish in water and KOH and inamyloid in Melzer’s, others (oleiferous hyphae) with a brownish to dark brown plasmatic pigment in water and KOH and dextrinoid in Melzer’s; lateral strata (15–) 20–50 (–60) μm thick, mediostratum (10–) 40–50 μm thick, consisting of a tightly adpressed, not gelatinized bundle of hyphae, 2–12 μm wide; in Congo red the mediostratum is darker than the lateral strata. Clamp connections absent (but a solitary clamp has been observed in the peripheral layer of the stipe trama). Hyphal system monomitic.
Habitat: Gregarious or scattered, growing in clayey soil among litter in tropical montane and lowland mixed forests dominated by Castanopsis fissa (Champion ex Bentham) Rehder & E. H. Wilson, Castanea henryi (Skan) Rehder & E. H. Wilson and Lithocarpus sp. with the presence of Schima superba Gardner & Champ. and Litsea rotundifolia var. oblongifolia (Nees) C.K. Allen, late spring to early autumn.
Index fungorum number: IF813027
Bayesian posterior probability (BPP) values (in bold) ≥ 0.7 and Maximum Likelihood bootstrap (MLB) values ≥ 50% are shown on the branches. Thickened branches indicate BPP ≥ 0.95 and MLB support ≥ 70%. Dashed branches indicate BPP ≥ 0.95 and MLB bootstrap support < 70%. Nodes that receive BPP < 0.95 but with ≥ 70% MLB are indicated by small black–filled circles. Accession numbers of the sequences retrieved from GenBank refer to Wu et al. (2014, 2015). Newly sequenced collections are in bold.
Figure 2. ITS phylogeny restricted to the major clade including Xerocomellus and Nigroboletus.
BPP values (in bold) ≥ 0.7 and MLB values ≥ 50% are shown on the branches. Thickened branches indicate BPP ≥ 0.95 and MLB support ≥ 70%. Dashed branches indicate BPP ≥ 0.95 and MLB bootstrap support < 70%. Nodes that receive BPP < 0.95 but with ≥ 70% MLB are indicated by small black–filled circles. Newly sequenced collections are in bold.