Hebeloma quercetorum (Photo: E. Grilli)

Taxonomy

Types: ITALY: Lazio, Parco Naz. Circeo (LT), Piscina delle Bagnatore (approx. 41.235°N, 13.064°E, alt. approx. 275 m a.s.l.) in meso-hygrophilous woodland under Carpinus betulus, Carpinus orientalis, Quercus cerris, Quercus frainetto and Quercus robur, 10 Nov. 1987, L. Quadraccia (Lectotype. herbarium acc. no. ROHB01218, HJB1000223; Isotype. herbarium acc. no. K(M)20803, HJB1000005). Lectotype designated by Grilli et al., Mycol. Prog. 15 (5) (1): (2015) ["2016"] page 35 (MBT202922).

• arrow_drop_downarrow_drop_upType notes
  The holotype originally designated was a mixed collection. A part of this mixed collection was designated as lectotype. The other part of the material represents H. cavipes. Note also that the “isotype” (K K(M)20803) represents a different taxon, H. celatum.

• arrow_drop_downarrow_drop_upEtymology
  From quercetum– oak forest, to emphasise the association with Quercus.

• arrow_drop_downarrow_drop_upOriginal diagnosis
  Pileus 25–75 mm, e subconvexo explanato-convexus vel passim explanatus, interdum depressus, margine +/- sinuoso, inflexo ex incurvo; cuticula laevigata vel corrugata, centro praesertim, sicca vel subviscosa, hygrophana saepe rore albido nitente, margine laevigato vel subcostato; siccus uno eodem modo cremeo-albidus, cremeo-flavus vel. Crustulinus, udus subgriseus vel griseo-brunneus +/- fuscus, exarescens discolor, centro obscuriore vel in media parte zonato, margine paulo clariore. Lamellae confertae ac sublatae (x 6–9 mm), rotundato sinuatae, lamellulae rotundatae; siccae, sporis numquam maculatae; ex albido-avellaneis, interdum colore carneo dilutis, subbrunneae, acie paulo clariore vel subconcolori, erosa. Stipes 35–90 (–125) x 5–10 (–12) mm, subcylindraceus, rectus vel subsinuosus, bulbo praeditus excentrico (usque ad 17 mm lato ); fibrosus ac fragilior, fistulosus, intus cuspide apicali praeditus, apice pruinosus, alibi in longitudinem fibrillosus; candidus, sericeus, tactu fuscescens. Cortina abest. Caro in medio pileo ac super lamellas subtilis. Odore nullo vel subraphanoideo in speciminibus recenter collectis, raphanoideo vel herbido-raphanoideo in sectis. Sapore subraphanoideo subamaro. Sporae (9–)10–13(–14) x 6–7(–7.5) μm, subcitriformes e amygdaliformibus, valde ac dense verrucosae, interdum cum perisporio passim disjuncto, subflavae sub microscopio optico, non dextrinoideae. Basidia 25–30 x 7–9 μm, tetrasporica. Cheilocystidia (25–) 30–80 (–85) pm, e lageniformibus cum apice obtuso vel subcapitulato, subcylindracea cum apice ± dilatato (x 4.5–9 μm, lato). Pleurocystidia adsunt. Caulocystidia cheilocystidiis similia, sed usque ad 120 μm longa, plerumque cum apice obtuso et basi ventricosiora (10–15 μm). Epicutis ex ixocute parum aucta constituta, quae quidem ex hyphis constat gracilibus (x 3–4 μm), saepe in pileocystidia claviformia vel sublagenliformia desinentibus. Cutis vix manifesta. Subcutis bene aucta, clare pseudoparenchimatica, ex hyphis aurantiacis constituta propter pigmentum membranarium incrustans. Habitat: in silvis deciduis, praecipue quercinis, litoralibus vel submontanis, thermo-mesophilis vel mesophilis (id est Quercus robur, Q. cerris, Q. frainetto) sed etiam Carpinus betulus cum Carpino orientali, Ostrya carpinifolia vel rarius cum Castanea sativa.

• arrow_drop_downarrow_drop_upEnglish translation
  Pileus 25–75 mm diam., subconvex to plano-convex or irregularly applanate, at times depressed, margin wavy, incurved to inflexed; surface smooth or wrinkled, especially at disc, dry or subviscid, often hygrophanous with a hoary look, margin smooth or slightly ribbed; when dry of a uniform whitish-cream, yellowish-cream or orange cream colour, when damp greyish or brownish-grey +/- dark, during dehydration discolouring, darker at disc or zonate over the inner limb, margin slightly lighter. Lamellae crowded and somewhat broad (× 6–9 mm), rounded with decurrent tooth, dry and never spotted; whitish-hazel, at times with pinkish shade, to 1ight brown, edge slightly lighter or subconcolourous, eroded. Stipe 35–90(–125) × 5–10(–12) mm, subcylindrical, straight or slightly wavy, with an eccentric bulb (up to 17 mm broad); fibrous and rather brittle, fistulose, with apical appendage; pruinose at apex, elsewhere lengthwise fibrillose; pure white, silky, becoming brown on handling. Cortina absent. Flesh thin both at pileus centre and on lamellae. Odour lacking or slightly raphanoid when collected, raphanoid or herbaceous-raphanoid on cutting. Taste bitterish, subraphanoid. Spores (9–)10–13(–14) × 6–7(–7.5) μm amygdaloid to sublimoniform, roughly and densely verrucose, at times with perispore just detached in some spots, light yellowish under the light microscope, not dextrinoid. Basidia 25–30 × 7–9 μm, four-spored. Cheilocystidia (25–)30–80 (–85) μm, lageniform, with blunt or subcapitulate apex, to subcylindrical with +/- broadened, apex (apex × 4.5–9 μm broad), generally ventricose at base (× 4–9 µm). Pleurocystidia absent. Caulocystidia like cheilocystidia but up to 120 μm long, generally lageniform, with blunt apex and more ventricose at base (× 10–15 μm). Epicutis a poorly developed ixocutis formed by thin hyphae (× 3–4 μm), often ending with clavate or sublageniform pileocystidia. Cutis not observable or hardly visible. Subcutis a well developed pseudoparenchymatic layer with orange encrusting pigment. Habitat: in coastal or submontane thermo-mesophilous or mesophilous deciduous forest, especially oak woodlands with Quercus robur, Q. cerris, Q. frainetto, occasionally with Carpinus betulus, C. orientalis. Ostrya carpinifolia and rarely Castanea sativa.

Description

Description of Hebeloma quercetorum based on 55 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (17) 21–50 (75) mm diameter; shape occasionally convex, umbonate or broadly umbonate, rarely umbilicate; characters occasionally rugulose, rarely pruinose; margin characters often smooth, rarely reflexed, involute, wavy, scalloped or sulcate; viscosity tacky when moist; colour variation usually unicolour, occasionally two color; colour at centre occasionally dark pinkish buff, rarely yellowish brown, honey, clay-buff, ochraceous, cinnamon, greyish buff, pinkish buff, orange-brown, warm buff, dark brick, cream, dark greyish buff or umber.

  Lamellae: attachment usually emarginate, rarely adnate or decurrent tooth; maximum depth 2–9 mm; number of complete lamellae 60–78; presence of tears often absent, occasionally visible with naked eye, rarely visible with x10 lens; white fimbriate edge often present, occasionally weak, rarely absent.

  Cortina presence: no.

  Stipe: (22) 35–66 (90) x 5–11 (65) {median} x (4) 5–12 (18) {basal} mm; stipe Q 0.3–9.8; base shape often cylindrical, occasionally clavate or bulbous, rarely tapering or subbulbous; floccosity occasionally floccose, fibrillose, pruinose at apex or velute, rarely pruinose, weakly floccose or none; rooting usually no, rarely yes or weak; thick rhizoids at base usually absent, rarely present;

  Context: Texture firm; stipe interior usually hollow, often superior wick, rarely stuffed; stipe flesh discolouring often no, occasionally weak, rarely yes; slenderness measure 3.6–17.5; smell often raphanoid, occasionally weakly raphanoid, rarely cocoa, odourless, earthy or strongly raphanoid; taste occasionally bitter, mild, raphanoid or weakly raphanoid where recorded.

  Spore deposit colour: usually brownish olive, occasionally greyish brown.

  Exsiccata characters: occasionally dark, lamellae blackening, pale or rich brown color.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, usually limoniform; colour in microscope occasionally yellow brown, brown or yellow, rarely brown yellow; guttules usually yes, rarely no or weak. papilla usually yes, rarely weak or very strongly; Spore Code: O2 O3; (P0) P1 P2; (D2) D3.

  Basidia: 26–36 (40) x 6–9 μm; ave. Q 3.1–4.2; spore arrangement 4 spored;

  Cheilocystidia: main shape ventricose, usually lageniform, occasionally cylindrical, rarely gently clavate or clavate-lageniform or clavate-ventricose; special features observed often septa, occasionally bifurcate, clamped septa or geniculate, rarely branching, many collapsed in exsiccata, median thickening or slender; cheilocystidia ratios: A/M = 1.04–1.22; A/B = 0.65–0.89; B/M = 1.36–1.78.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 200 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation often yes, occasionally no; shape of trama elements beneath subcutis often ellipsoid or thickly sausage-shaped, occasionally angular, cylindrical, isodiametric or thinly sausage-shaped up to 20 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 120 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma quercetorum's preferred habitat appears to be deciduous woodland or deciduous, Mediterranean woodland with calcareous soil and litter. Where only one possible associate was recorded, the most commonly recorded associate was Quercus (96.9%) but Pinus (3.1%) were also recorded. In these cases the most commonly recorded family was Fagaceae (96.9%). We have additional records where Carpinus (18.0%), Cistus (6.0%), Populus (2.0%), Betula (2.0%) and Ostrya (2.0%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Fagaceae (94.0%), Betulaceae (22.0%), Pinaceae (10.0%), Rosaceae (10.0%) and Cistaceae (6.0%) The growth habit of our collections was occasionally scattered, gregarious or solitary and rarely caespitose or connate.

  According to our current collections, the species is predominantly found in Europe (98.2%) but also found in Temperate Asia (1.9%). On these continents, collections has been found in the WWF biomes The World Wildlife Fund (WWF) have divided the world into 867 terrestrial ecoregions. The ecoregion here is estimated by mapping from the GPS coordinates of the collection using data made available by Dinerstein et al (2017). Use this webtool to explore the ecoregions visually or see a full list of current ecoregions on Wikipedia. mediterranean forests, woodlands & scrub (85.2%) and temperate broadleaf & mixed forests (13.0%), specifically including the ecoregions: Northeast Spain and Southern France Mediterranean forests (31.5%), Italian sclerophyllous and semi-deciduous forests (27.8%), Tyrrhenian-Adriatic sclerophyllous and mixed forests (14.8%) and Appenine deciduous montane forests (11.1%). From collector information, it appears collections have been found only in the 1.4 Forest – Temperate IUCN habitat We map from the collector's description of the habitat to the International Union for Conservation of Nature (IUCN)'s definition using a standardised set of rules. Please see this page for a full list of IUCN habitats..

  Within Europe we have records from the Southwest (Spain, Italy, Portugal and France) and the Southeast (Italy and North Macedonia). Specimens have been collected from 38.1°N to 44.5°N.

  Within Temperate Asia all our records are from Western Asia (Cyprus).

• arrow_drop_downarrow_drop_upMolecular results
  As for the other species of the quercetorum-complex, H. quercetorum is distinct and can be identified based on each of the tested loci apart from ITS. The assignment of the name H. quercetorum to this taxon is supported by ITS, V6 and V9 sequences obtained from the lectotype (Grilli et al. 2016). There are two published ITS sequences from Asia (Iran, Mongolia that are likely to belong to a member of the quercetorum-complex (FR852300; FJ803967 with Populus davidiana).

• arrow_drop_downarrow_drop_upCommentary
  Hebeloma quercetorum has a mixture of differently shaped cheilocystidia. This taxon has ventricose or lageniform cheilocystidia that are mixed with cylindrical cheilocystidia and occasional more gently clavate cheilocystidia, wider at the apex and tapering below. There are also usually a few intermediates which are clavate-lageniform, i.e. swollen both at the apex and in the basal part. With a large number of ventricose (lageniform) cheilocystidia, the distinctly ornamented, rather strongly dextrinoid spores plus the absence of any obvious cortina or veil, this taxon could belong to either H. sects. Sinapizantia or Velutipes. Within H. sect. Sinapizantia, and with the large number of ventricose cheilocystidia, it can be confused with H. sinapizans. However, it is easily separated from H. sinapizans: macroscopically, by the occasional presence of tears, the lower number of lamellae and the less robust appearance; microscopically, by the presence of occasional gently clavate and clavate-lageniform cheilocystidia. Both these taxa have a cheilocystidium ratio B/M that is at least 1.35. With H. sinapizans this ratio usually exceeds 1.5, but with H. quercetorum this ratio depends on the balance between the different types of cheilocystidia present and measured. Within H. sect. Velutipes, Hebeloma quercetorum is a member of the quercetorum-complex and hence is closely related, both phylogenetically and morphologically, to H. erebium and H. celatum. With regard to H. erebium there is a clear biogeographical separation. We have no records of H. erebium further south than the latitude of 48 deg N while we have no ecords of H. quercetorum further north than latitude 44.5 deg N. Of course it is possible that H. erebium may occur further south, but if so we would expect it to occur in higher altitude areas. Also of note is that H. quercetorum appears to be restricted to Quercus as a host whereas H. erebium has been recorded with many different hosts. Further, H. quercetorum has a far thicker epicutis than H. erebium, in the range 160–200 μm, while H. erebium has its epicutis thickness in the range 60–80 μm. The cheilocystidia of H. quercetorum are more regularly lageniform to ventricose to cylindrical than both H. erebium and H. celatum which have more cheilocystidia that are clearly gently clavate or clavate-lageniform. This is reflected in the cheilocystidium ratio A/M, which for H. quercetorum is at most 1.22 and for H. celatum, in particular, is never less than 1.25. With respect to H. celatum, which also appears to favour Southern Europe but does also occur in Northern Europe, the latter species tends also to have a more robust appearance. Macroscopically, H. quercetorum also appears close to H. aestivale and originally Vesterholt (2005) placed both these taxa in H. subsect. Aestivalia. They do also favour very similar habitats; one macroscopic difference, which can be useful in the field ,is the number of full length lamellae (L), for H. aestivale this is 35–59 with average 50 while for H. quercetorum L = 62–79 with average over 66. Microscopically, these two taxa are very easy to separate both on the cheilocystidia which are quite different and the spores where H. aestivale has a strongly and constantly loosening perispore. We suspect that this taxon was in the past often confused with H. sinapizans, which was therefore considered more variable than it is. Quadraccia (1993) realized the difference and established his species H. quercetorum. He placed this species in H. subsect. Sinapizantia. He stated: “H. sinapizans may look vaguely like H. quercetorum however the former is different in colour and shape of sporocarps, the striking raphanoid smell and the taste likewise raphanoid and bitter and, above all, in microscopic features such as the larger, strongly dextrinoid spores with almost smooth snout like apex and the distinctly lageniform cheilocystidia”. Intriguingly, Quadraccia considered the spores of his collection of H. quercetorum to be indextrinoid; we have examined this material and disagree. However, it is certainly true that the spores of H. sinapizans are more consistently strongly dextrinoid (D3, D4) than those of this taxon which are distinctly to rather strongly dextrinoid ((D2)D3). As was pointed out by Grilli (herbarium note), the holotype material for this taxon was mixed. The part of the collection that was not H. quercetorum is H. cavipes. Furthermore, the isotype that was deposited at Kew actually represents the species H. celatum as mentioned in our description of that species.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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