Alessioporus ichnusanus (Alessio, Galli & Littini) Gelardi, Vizzini & Simonini, in Gelardi et al., Mycologia 106(6): 1171 (2014)
Basidiomes small to medium-small. Ontogenetic development secondary angiocarpic. Pileus (2–)3– 11(–13) cm diam., at first hemispherical then convex and finally pulvinate-flattened to vaguely depressed at center, moderately fleshy, firm at the beginning but progressively softer with age; margin initially coalescent with the stipe cortex but soon disrupting and curved downwards, typically wavy and lobed until maturity, then progressively expanding and regular or uplifted, not or only slightly extending beyond the tubes; surface matt, dry, very finely tomentose to glabrous, not areolate; cuticle ochreous (5C8–5D5), ochraceous-brown (6D8–6E5) to brownish-olive-gray (5E8– 5F4, 6F8–6F4), sometimes with copper red hues (7–8D7 to 7–8F8), evenly ornamented with radially arranged, brownish or dark brown to nearly blackish-brown fibrils; slowly and barely darkening on handling and finally becoming sordid blackish-brown (5F2, 5–6F3, 7–8F3 to 7–8F6); subcuticular layer whitish. Stipe (3–)4–11(–13) × 1–3(–5) cm, as long as or a little longer than the pileus diam. at maturity, central to slightly off-center, solid, firm, dry, straight to curved or sinuous, initially ventricose-fusiform then cylindrical or rarely enlarged downwards or faintly clavate but usually attenuate at the apex and always tapering at the very base, moderately to strongly rooting; surface covered with a rough and longitudinally stretched reticulum or coarsely ribbed lengthwise, or rarely appearing smooth throughout, exhibiting a prominent but narrow granular pseudo-annular zone in the lower or middle part, the latter only occasionally being absent, smooth in the lower quarter; yellowish-cream (4A8–4B6) then yellowish-brown in age (5–6C8 to 5–6D6) but of a brighter yellow at apex and on ribs (3A7, 3A8), dark red (9D8–9D6), reddish brown (8D8–8D6) to brown (8-9E8 to 8–9E5) in the lower half and gradually darker towards the base, bruising blue then sordid blackish-brown when pressed; basal mycelium whitish-gray. Context firm and tough when young, later soft textured in the pileus, up to 2 cm thick in the central zone, a little more fibrous in the stipe, whitish in the pileus (2-3A2) but sometimes pinkish below the cuticle (6–7A2), yellowish (2–3A3 to 2–3B3) in the stipe but gradually darker (2–3A4 to 2– 3B4) downwards, rhubarb red to brownish-black (10–11D8 to 10–11F7) at the base; immediately turning blue throughout after sectioning and finally fading to drab yellowish; yellowish-orange to rusty-red or brown where eaten by slugs and with pinkish hues where eroded by maggots; subhymenophoral layer pale yellowish; dried material with brownish pileus and hymenophore, dirty yellow to ochraceous elsewhere. Tubes at first thin then broader and usually as long as the thickness of the pileus context (up to 1 cm long), adnate to depressed around the stipe apex and shortly decurrent with a tooth, bright yellow (3A7, 3A8) to olive yellow (3B8–3D7) and finally olive green (3E7, 3E8), bruising blue when cut. Pores initially even, later with a convex surface, small at first then gradually wider (up to 0.2 cm diam.), simple, roundish to angular, concolorous with tubes, turning blue when bruised and eventually fading to drab brown, at maturity with russet-brown stains at the pore edge. Smell faintly fruity, agreeable. Taste mild. Spore print olive-brown. Macrochemical reactions. NH4OH: staining rusty brown on hymenophore, no reaction elsewhere. KOH: staining dark red on pileus, dark reddish-brown on hymenophore and stipe, pinkish on pileus context, orange on stipe context but reddish-brown at the base. FeSO4: staining pale yellow on context, no reaction elsewhere; weak “fleeting-amyloid” reaction observed with Melzer’s solution on hymenophoral trama.
Basidiospores [474/24/14] (12.0–)13.3 ± 0.8(–14.0) × (5.5–)5.7 ± 0.3(–6.5) μm, Q= (2.19–)2.36 ± 0.12(–2.59), V= 226 ± 34 μm³, inequilateral, ellipsoidal to elliptical-fusoid or subcylindrical in side view, ellipsoid in face view, smooth, with a pronounced apiculus and shallow 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 weakly dextrinoid, acyanophilic and showing a faint metachromatic reaction. Basidia (29–)31–40(–51) × (8–)10–12(–16) μm (n= 30), cylindrical-clavate to clavate, moderately thickwalled (0.5–1.0 μm), predominantly 4-spored but also 3-, 2-, or 1-spored, with relatively long sterigmata (3–6 μm), hyaline to pale yellowish and containing straw-yellow oil guttules in water and KOH, without basal clamps; basidioles subclavate to clavate, about the same size as basidia. Cheilocystidia (35–)37–61(–65) × 7–11 μm (n= 17), common, projecting straight to sometimes flexuous, cylindrical-fusiform to ventricose-fusiform or otherwise lageniform, with long neck and rounded tip, smooth, moderately thick-walled (0.5–1.0 μm), hyaline to pale yellowish or rarely brownish-yellow in water and KOH, straw yellow (inamyloid) in Melzer’s, without epiparietal encrustations. Pleurocystidia (38–) 45–70(–80) × 8–13 μm (n= 29), frequent, color, dimensions, shape and chemical reactions as in cheilocystidia; 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 [182/20/9] (42.0–)46.4 ± 3.9(–54.5) × (7.5–)8.2 ± 0.4(–9/0) μm, Q= (5.30–)5.90 ± 0.57(–7.12), cylindrical, apex rounded-obtuse, usually enlarged and with occasional protrusions, moderately thick-walled (up to 1 μm), nearly hyaline to pale yellowish in KOH, smooth or seldom ornamented with subtle granular epiparietal encrustations; subterminal elements similar in shape, color and dimensions to terminal elements. Stipitipellis a texture of slender, loosely intermingled and longitudinally running, smooth walled, adpressed hyphae, 3-11 μm across, hyaline in water and KOH; the stipe apex covered by a well-developed caulohymenial layer consisting of sterile caulobasidioles, fertile spore-bearing caulobasidia and scattered projecting caulocystidia similar in shape, color, dimensions and chemical reactions to hymenial cystidia. Lateral stipe stratum under the caulohymenium present and well differentiated from the stipe trama, of the “boletoid type” at the stipe apex a 50–130 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, subparallel to loosely interwoven, filamentous, smooth, inamyloid hyphae, 5–15 μm broad, hyaline to very 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 (2–)4–7 μm apart, hyaline in water and KOH, inamyloid in Melzer’s; lateral strata 30–50 μm thick, mediostratum 15–20 µm thick, consisting of a tightly adpressed, not gelatinized bundle of hyphae, 2–13 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, 2–10 μm broad, wall up to 1.0 μm thick, hyaline to yellowish in water and KOH. Clamp connections absent in all tissues. Hyphal system monomitic. Edible.
Habit, ecology, phenology, distribution: Solitary to gregarious or more often caespitose, sometimes with basidiomes arising from the stipes of adjacent basidiomes, 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) and to a lesser extent Cistus spp., rarely with Castanea sativa and perhaps with the exotic Eucalyptus camaldulensis, also reported with Pteridium aquilinum (Tentori 2006), on dry soil, ubiquitous, summer to early autumn. Reported from southern Europe, uncommon to rare.
Index Fungorum number: IF 808530
Notes: Formally described as a new Xerocomus species by Alessio (1984), Alessioporus ichnusanus was first found in Sardinia by the Italian mycologist R. Galli in 1980 and initially reported as an unknown species (Galli 1981). It was since recorded from several different places in Sardinia (Galli 1987; Brotzu 1988, 1993; Foiera et al. 1993; Brotzu and Colomo 2009), Sicily and mainland Italy (Morara 1988; Simonini and Fiandri 1988; Alessio 1991; Migliozzi and Coccia 1991; Redeuilh and Simonini 1995, 1999; Lavorato 1996; Gennari 1997, 2005; Chevtzoff 1998; Galli 1998, 2007, 2013; Ladurner and Simonini 2003; Cazzoli 2006; Tentori 2006; Zuccherelli 2006; Consiglio and Papetti 2009; Gelardi 2010; Illice et al. 2011; Rodà 2012) and from several European countries, mostly in the Mediterranean, viz. France (Chevtzoff 1998; Redeuilh and Simonini 1999; Eyssartier and Roux 2011), Spain, including the Balearic Islands (Águeda et al. 2006; Ruiz Fernández and Ruiz Pastor 2006; Calzada Domínguez 2007; Muñoz et al. 2008), Bulgaria (Assyov and Stoykov 2011b) and Greece, including the Cyclades Islands (Constantinidis 2009; Polemis et al. 2012), with a single finding in Austria (AMS 2009).
Alessioporus ichnusanus is a medium-small sized species, exhibiting an ochraceous-brown to dark olivaceous-brown fibrillose pileus, sometimes with copper red hues and a wavy margin at least in young specimens, a yellow to olive colored hymenophore and a stout, deeply rooting stipe covered with a rough and darker net that is very rarely absent, as reported by Chevtzoff (1998), Taylor et al. (2001, 2002) and Galli (2007, 2013), bright yellow at the apex, dark red-brown to blackish-brown elsewhere and with a whitish-gray basal mycelium. The context is whitish in the pileus, yellowish in the stipe with reddish shades, purplish-red to brownish-black at the base, turns uniformly blue on exposure, as do the external surfaces after injury or bruising. Such strong discoloration, caused by auto-oxidation, is unlike the light blue staining of most Xerocomus species (Alessio 1985). The most important morphological character is the narrow, granular ring-like zone in the middle or lower half of the stipe, formed by the remnants of the connection between the pileus margin and the stipe cortex during the primordial stage. Other observations indicate highly variable spore size, sometimes with aberrant basidiospores more than 20 μm or even up to 28–30 μm long (Alessio1984, 1985; Simonini and Fiandri 1988; Brotzu 1993; Foiera et al. 1993; Chevtzoff 1998; Lannoy and Estadès 2001; Galli 2007, 2013; Brotzu and Colomo 2009).
Lavorato (1991) and Contu (pers. comm.) suggested that Boletus siculus Inzenga (Inzenga 1869) might be an older name for A. ichnusanus. Unfortunately, no type material was preserved for B. siculus and there is no evidence to support their conspecificity.
Alessioporus ichnusanus was misinterpreted as a reticulate phenotype of Boletus pulverulentus Opat. (Cetto 1980, 1982; Angarano 1990), and perhaps with B. poikilochromus Pöder, Cetto & Zuccherelli (Cetto 1983), since the same provisional name of B. pulverulentus f. reticulatipes has been given to both of them. Apart from the reticulum, B. pulverulentus differs from A. ichnusanus by its slender, xerocomoid appearance, stronger bluing overall, narrower spores with a Q value of 2.6–2.9 and the nearly sterile stipe (Alessio 1985; Breitenbach and Kränzlin 1991; Lannoy and Estadès 2001; Muñoz 2005; Watling and Hills 2005; Galli 2007; Klofac 2007; Šutara et al. 2011). Boletus poikilochromus shares with A. ichnusanus the boletoid appearance and strongly bluing tissues, but differs mainly by the tendency of the basidiomes to fade to cinnamon-brown with age, its very peculiar smell and noticeably smaller spores (11.7 × 4.7 µm in average) (Lannoy and Estadès 2001; Muñoz, 2005; Galli 2007; Klofac 2007; pers. obs.).
Boletus rainisii A.E Bessette & O.K. Miller occurs in North America and is discriminated by the dark olivaceous-brown pileus, bright yellow smooth stipe with reddish hues at the extreme base, darker blue staining reaction throughout, shorter pileipellis terminal cells that are covered with brown encrustations, sterile stipe surface and its association with conifers (Bessette et al. 2000). The Chinese B. sinopulverulentus Gelardi & Vizzini is readily distinguishable by the smaller size, entirely dark brown stipe that is finely scabrous-scissurate radially so as to resemble a zebra-pattern, stronger blue staining reaction, non-rooting stipe, nearly sterile stipe surface and smaller spores (Gelardi et al. 2013).
Alessioporus ichnusanus is an edible species but curiously Brotzu and Colomo (2009) refer to it as probably poisonous. It was keyed out in several regional mycotas and bolete monographes, such as Engel et al. (1996), Estadès and Lannoy (2004), Horak (2005), Muñoz (2005), Klofac (2007), Boccardo et al. (2008), Rödig (2012), and it is undoubtedly a well-characterized species, unlikely to be confused with any other taxa. The only incorrect attribution we have found is a misinterpretation as B. fragrans Vittad. (Pérez-De-Gregorio 2000). Because of its rarity, A. ichnusanus was recently included in the Red List of Italian macrofungi (Rossi et al. 2013).
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.