Pulchroboletus roseoalbidus (Alessio & Littini) Gelardi, Vizzini & Simonini, in Gelardi et al., Mycologia 106(6): 1176 (2014)
Basidiomes small to medium-small sized. Ontogenetic development secondary angiocarpic. Pileus (1) 2–10(–12) cm diam., at first hemispherical then persistently convex and finally pulvinate flattened to vaguely depressed at centre, moderately fleshy, firm when young but progressively softer with age; margin initially involute and coalescent with the stipe cortex but soon disrupting and curved downwards, then progressively expanded or uplifted, regular to faintly sinuate or lobed, not or only slightly exceeding beyond the tubes (up to 0.1 cm); surface matt, dry but slightly greasy in moist weather, very finely tomentose but becoming glabrous in aged specimens, not areolate; cuticle at first pastel pink (7A4–7C3, 8A4–8C3, 9A3–9B2), gradually bleaching to pale pink (10–12A3 to 10–12A2, 13–15A2), cream-pinkish (6A4, 6A3), pinkish-beige (6–7B3 to 6–7C2) or whitish-pink (5–6–7A2), sometimes with darker pigmented, pinkish-purple areas or spots (10–11C5 to 10–11D4), occasionally uniformly blood red or vinaceous red (8–10C8 to 8–10C7, 10–11D8 to 9–11E7); nearly unchangeable or staining deep purple-red when rubbed, bluish when injured; subcuticular layer pinkish-purple. Stipe (2–)3–9(–11) × (0.5) 1–3(–7) cm, as long as or a little longer than pileus diameter at maturity, central to slightly off-center, solid, firm, dry, straight to curved or sinuous, generally narrowing downwards, rarely cylindrical, ventricose-fusiform or flattened, occasionally subclavate but always pointed at the very base, conspicuously rooting; surface smooth to fibrillose, without reticulum or only sporadically with a rough, elongated net, with a prominent but narrow granular pseudo-annular zone in the middle or upper part, such ornamentation being sometimes undetectable; bright yellow at apex (3A7, 3A8), yellowish elsewhere (4A6, 4A3) but covered with fine and scattered, reddish to purple- red punctuations, more pronounced towards the base, reddish-brown (8-9D8 to 8-9E7) at the base in old basidiomes, bruising blue then sordid blackish-brown on handling. Context firm and tough in youth, later soft textured in the pileus (up to 2.3 cm thick in the central zone), more fibrous in the stipe, pinkish-lilac (12–14B4 to 12–14B2) in the pileus, particularly bright beneath the cuticle and above the tubes, yellow (2–3A2 to 2–3A3) in the stipe but gradually darker (2–3A4) downwards; immediately turning blue in the stipe and above the tubes but nearly unchangeable in the rest of the pileus when exposed to air, after several hours fading to creamyellowish in the pileus and dirty ochraceous in the stipe; reddish-purple where eaten by slugs in the pileus and with pinkish-purple hues in tissues eroded by maggots; subhymenophoral layer pinkishlilac; dried material with whitish-pink pileus and brownish hymenophore, reddish-brown on stipe, dirty yellow to ochraceous on context. Tubes at first thin then increasingly broader and usually longer than pileus context thickness (up to 1.8 cm long), adnate to depressed around the stipe apex and shortly decurrent with a tooth, at times subdecurrent, bright yellow (3A7, 3A8) to olive yellow (3B8–3D7) and finally olive green (3E7, 3E8), bruising blue on cutting. Pores initially forming a flat surface, later convex, small at first then distinctly wider (up to 3 mm diam), simple, roundish to angular, concolorous with tubes, turning blue on bruising and eventually fading to drab brown, at maturity with russet-brown stains at the pore edges. Basal mycelium whitish. Spore print olive-brown. Smell faintly fruity, agreeable. Taste mild. Macro chemical reactions: NH4OH: staining rusty brown on hymenophore, orange on stipe surface, none elsewhere (the pinkish-lilac tint in pileus context is bleached away); KOH: staining dark red toreddish-brown on pileus and stipe, dark reddish-brown on hymenophore, pinkish on pileus context, orange on stipe context but reddish-brown at the base; FeSO4: staining pale olive-green throughout; weak ‘fleeting-amyloid’ reaction observed with Melzer’s solution on hymenophoral trama.
Basidiospores [361/20/12] (13.5–)14.7 ± 0.8(–16.0) × (6.5–)6.8 ± 0.3(–7.5) μm, Q= (1.97–)2.17 ± 0.11 (2.30), V= 359 ± 39 μm³, inequilateral, broadly ellipsoidal to less frequently ellipsoid-fusoid in side view, broadly ellipsoid in face view, smooth, with a pronounced apiculus and shallow to moderately marked suprahilar depression, with rounded apex, moderately thick-walled (0.5–1.0 μm), straw-yellow colored in water and KOH, having one, two or more frequently three large oil droplets when mature, inamyloid to moderately dextrinoid, acyanophilic and with an ortochromatic reaction. Basidia (23–) 30–50(–53) × (10–)12–15(–19) μm (n= 25), cylindrical to cylindricalclavate, rarely truly clavate, moderately thick-walled (0.5–1.0 μm), predominantly 4-spored but frequently also 3-, 2-, or 1-spored, with relatively long sterigmata (3–6 μm, although 15 μm long sterigmata were observed on one anomalous basidium), hyaline to pale yellowish and containing straw-yellow oil guttules in water and KOH, without basal clamps; basidioles clavate, about the same size as basidia. Cheilocystidia (32–)38–66(–68) × 6–12 μm (n= 20), common, projecting straight to sometimes flexuous, fusiform to subcylindrical or rarely ventricose-fusiform, with long neck and rounded tip, occasionally clavate, smooth, moderately thick-walled (0.5–1.0 μm), hyaline to pale yellowish in water and KOH, straw yellow (inamyloid) in Melzer’s, without epiparietal encrustations. Pleurocystidia (40–) 59–76(–80) × (8–) 12–18(–20) μm (n= 25), color, shape and chemical reactions as in cheilocystidia, but slightly longer and distinctly broader, predominantly ventricose-fusiform (a single cystidium with a diverticulate tip was observed), infrequent; pseudocystidia not observed. Pileipellis a trichoderm consisting of strongly interwoven, filamentous and sinuous, often branched hyphae not constricted at septa, tending to be repent in the outermost layer and thus turning into a cutis partially embedded in gelatinous matter; terminal elements [259/20/10] (30.0–)44.2 ± 8.4(–55.5) × (7.0–)8.0 ± 0.4(–8.5) μm, Q= (4.01–)5.67 ± 0.95(–7.14), cylindrical, some short and acorn-shaped or bullet-shaped, occasionally cystidioid, apex roundedobtuse and enlarged or tapered, moderately thick-walled (0.5–1.0 μm), nearly hyaline to pale yellowish in KOH, smooth or rarely ornamented with subtle granular 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, 3–11 μm wide, hyaline in water and KOH; the stipe apex covered by a well-developed caulohymenial layer consisting of sterile caulobasidioles, fertile spore-bearing caulobasidia and projecting caulocystidia similar in shape, color, dimensions and chemical reactions to the pleurocystidia. Lateral stipe stratum under the caulohymenium present and well differentiated from the stipe trama, of the “boletoid type”, at the stipe apex a 40–80 μm thick layer consisting of divergent, inclined and running towards the external surface, loosely intermingled and unbranched or sparingly branched hyphae remaining separate from each other and 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, inamyloid hyphae, 2–13 μm broad, hyaline to pale yellowish in water and KOH. Hymenophoral trama bilateral-divergent of the “Boletus-type”, with moderately to distinctly divergent and loosely arranged, gelatinized hyphae, lateral strata hyphae in transversal section remaining separate and (1– )4–7(–10) μm apart, hyaline in water and KOH, inamyloid in Melzer’s; lateral strata (10–)15–40 μm thick, mediostratum 15–40 µm thick, consisting of a tightly adpressed, not gelatinized bundle of hyphae, 3–13 µm wide; in Congo Red the mediostratum is darker than the lateral strata; oleiferous hyphae present. Basal mycelium consisting of subparallel to loosely intermingled, densely arranged, unbranched, filamentous, sinuous, inamyloid, smooth-walled hyphae, 3–17 μm broad, wall up to 1.0 μm thick, hyaline to pale yellowish in water and KOH. Clamp connections absent in all tissues. Hyphal system monomitic. Edible.
Habit, ecology, phenology, distribution: Solitary to gregarious, more often caespitose or branched, with specimens rising from the stipe of adjacent basidiomes or with two stipes merging into a single pileus, in warm Mediterranean regions, growing in association with Quercus spp. (Q. ilex, Q. suber, Q. coccifera, Q. cerris, Q. robur, Q. pubescens, Q. petraea, Q. pyrenaica, Q. frainetto), also with Cistus spp., rarely with Castanea sativa, on dry soil, ubiquitous, summer to early autumn. Reported from southern Europe, rare.
Index Fungorum number: IF 808532
Notes: Pulchroboletus roseoalbidus was described (in Xerocomus) in early 1987 from collections made by M. Sarnari and G. Littini, in central Italy and and V. Carcò and E. Mendolia in Sardinia (Alessio 1987, 1990). A few months later, the same taxon was published under the name Pulveroboletus albopruinosus Cetto & Zuccherelli (Cetto 1987). Since then, this species was reported from insular and peninsular Italy (Simonini and Fiandri 1989; Littini 1992; Foiera et al. 1993; Zuccherelli 1993 as P. albopruinosus; Gennari 1994, 2005; Redeuilh and Simonini 1995; Galli 1998, 2007, 2013; Contu 1999; Lavorato and Rotella 1999; Consiglio and Papetti 2001; Cazzoli 2002, 2006; Migliozzi and Camboni 2002; Ladurner and Simonini 2003; Venturella 2004; Tentori 2006; Brotzu and Colomo 2009), and from other European and extralimital countries, such as France (Corsica) (Anonymous 1989; Alessio 1991; Roth 1994; Lannoy and Estadès 2001; Eyssartier and Roux 2011), Spain, including the Balearic Islands (Moreno et al. 1995; Ruiz Fernández 1997 as X. calañiensis; Pardo et al. 2004; Calzada Domínguez 2007; Muñoz et al. 2008), Hungary (Károly 2006), Bulgaria (Assyov and Denchev 2009; Denchev and Assyov 2010) and Greece, including the Cyclades Islands (Constantinidis 2009 as “Rubinoboletus roseoalbidus”; Polemis et al. 2012). Pulchroboletus roseoalbidus is circumscribed by its medium-small size, pale pastel pink, creampink to whitish with pinkish hues or rarely evenly blood red pileus, yellow to olive hymenophore, tapered and deeply rooting yellow stipe covered with reddish punctuations, especially in the lower half, whitish basal mycelium, a yellowish context that is bright pinkish-lilac in the peripheral zones of the pileus (at times pinkish overall in the pileus) and tissues quickly that bruise blue on injury. The stipe of P. roseoalbidus is generally devoid of reticulum, although a narrow ring-like pattern of coarse granules is nearly always visible, but sometimes it is ornamented by a rough net or ribs arranged lenghtwise (Foiera et al.1993; Lannoy and Estadès 2001; Consiglio and Papetti 2001; Cazzoli 2002; Migliozzi and Camboni 2002; Ladurner and Simonini 2003; Cazzoli 2006; Calzada Domínguez 2007; Galli 2007). Basidiospores are uniformly broad (~7 μm in average) and, as was reported for A. ichnusanus, oversized spores were observed for P. roseoalbidus, with dimensions reaching 25 μm long and 9 μm wide (Alessio 1987, 1990; Migliozzi and Camboni 2002; present study). Some authors (Cetto 1987; Moreno et al. 1995; Contu 1999) report a blue violet amyloid reaction of the stipe trama with Melzer’s solution. However, such a reaction was not observed in our material and we suggest it may be occasional or inconsistent.
In the original diagnosis of P. albopruinosus the only major discrepancy was the spore size, which is dramatically smaller than that of P. roseoalbidus (Cetto 1987). This divergence, however, was later shown to be measurement error (Alessio 1990). The taxonomic attribution to the genus Pulevoroboletus is also questionable, because it was based on the presumed solubility of the yellow pigment of the hymenium, a character not included in the delimitation of the genus (Singer 1986) and moreover not detected on P. albopruinosus specimens (Simonini and Fiandri 1989). Simonini and Fiandri (1989) stressed that Boletus rigelliae Velen. (Velenovský 1922) might represent an older name for P. roseoalbidus, but as already pointed out by Alessio (1985, 1991), the former is most likely conspecific with Aureoboletus gentilis (Quél.) Pouzar. Despite its distinctive features, P. roseoalbidus is morphologically similar to the eastern North American species Boletus patrioticus Baroni, A.E. Bessette & Roody, but differs from the latter by the dark red to brownish-olivaceous-red pileus, slight blueing in the context above the tubes and only erratically elsewhere, different pileipellis arrangement and smaller spores; additionally, B. patrioticus lacks the ring-like zone on the stipe and its growth is never caespitose (Baroni et al. 1998; Bessette et al. 2000).
Amongst European species, Xerocomus bubalinus (Oolbekkink & Duin) Redeuilh (?= X. erubescens Cadiñanos & Muñoz) shares with P. roseoalbidus the noticeably pinkish tint beneath the cuticle but is discriminated by the dark reddish-brown pileus, gradually fading to ochraceous-buff, context turning light blue just above the attachment with the tubes and in the pileus-stipe connection zone, distinctly smaller spores, different pileipellis stucture, non-caespitose growth and association mainly with Populus spp. and Tilia spp. in wet habitats (Oolbekkink 1991; Muñoz et al. 2008; Gelardi 2009; Assyov and Stoykov 2011a; Knudsen and Taylor 2012).
Xerocomus rubellus Quél. is a more vividly colored species characterized by very bright red pileus and stipe, light blue oxidation on external surfaces, uniformly yellow context with carrot orange punctuation at the stipe base and discoloration to light blue only above the tubes, smaller spores, different pileipellis stucture and a growth habit that is never caespitose (Engel et al. 1996; Lannoy and Estadès 2001; Watling and Hills 2005; Klofac 2007; Muñoz et al. 2008; Šutara et al. 2011). As with A. ichnusanus, P. roseoalbidus was included in many European bolete field guides and regional taxonomic treatments (Engel et al. 1996; Taylor et al. 2002; Estadès and Lannoy 2004; Horak 2005; Muñoz 2005; Klofac 2007; Eyssartier and Roux 2011; Rödig 2012).
Figure 1. Hypoboletus group (Nuhn et al. 2013). Bayesian phylogram obtained from the combined ITS-LSU-tef-1α sequence alignment. Bothia castanella was used as the outgroup taxon. BPP values over 0.75 (in bold) and MLB values over 50% are shown above clade branches. Newly sequenced collections are in bold.