Hebeloma theobrominum (Photo: J. Vesterholt)

Taxonomy

• arrow_drop_downarrow_drop_upNomenclatural notes
  Misapplied name: Hebeloma truncatum (Schaeff.) P. Kumm. Führ. Pilzkde: 80 (1871); nom. illegit. (Art. 52.1), s. auct.; non Rhodocybe truncata (Schaeff.) Singer, Mycologia 38: 687 (1947) [“1946”]

Types: ITALY: Lazio, Manziana (approx. 42.13°N, 12.13°E, alt. approx. 370 m a.s.l.) in deciduous woodland under Quercus cerris and Quercus frainetto, 16 Oct. 1984, L. Quadraccia (Holotype. herbarium acc. no. ROHB 00925, HJB1000080).

• arrow_drop_downarrow_drop_upEtymology
  Named after Theobroma cacao, the cocoa tree, to emphasise the colour of the pileus.

• arrow_drop_downarrow_drop_upOriginal diagnosis
  Pileus 30–45 (–50) mm latus, carnosus, elasticus, non parum abnormis, primitum subhemisphericus margine involuto, mox convexus, dein quasi applanatus, semper lato umbone obtuso praeditus et margine ex incurvo usque ad inflexum, interdum mediocriter gibbosus et margine subsinuato. Cuticula aequalis, glabra, subviscida, paene roro albido nitens. Margo in iuvenibus subpruinosus et mediocriter sulcatus. Color fere aequalis, cacainus, rufo-cacainus, badius, interdum in disco subpallescens, paene avellanea-ochraceus. Lamellae confertae, haud latae (3–5 mm), rotundato-adnexae, lamellulis subtruncatis interpositis, siccae vel subplorantes guttulas aquosas in iuvenibus, sed numquam sporeis maculatae, acie minute crenulata, pruinosa, albida, colore plerumque claro, ex albido ad fusco-ochraceum pallidum usque ad argillaceo-brunneolum vel ochraceo-ferrugineum, interdum cretaceo-incanum. Stipes 30-50 x 7–10 (–12) mm, solidus, subcylindricus, nonnunquam basim versus modice attenuatus; plane fibrilloso-striatus, dense pruinosus de summo paene ad infimum, densa pruina conspersus; plenus vel fistuloso-cuspidatus; aequabiliter candidus albisque vix fuscescens. Cortina nulla in ipsis immaturis speciminibus. Caro pilei plana alba, vix stipitis fuscescens praesertim in basi; odore subraphanoideo in speciminibus recenter collectis, raphanoideo in sectis; sapore raphanoideo subamaro. Sporae (8) 8,5–10,5(–11) μm, amygdaliformes elongate, apice saepe oblongo-papillato, laeves vel puncticulatae in ammonio hydroxido, kalii hydroxido et chloralii hydroxido, tenui colore flavo sub microscopio optico, dextrinoideae. Basidia tetrasporica 25–30 x 7–8 μm. Cellulae marginales (20) 30–45 (60) x 4–6 μm, subcylindaceae vel clavato-capitulatae saepe apice incrassatae, x 7–9 μm. Cellulae caulinares marginalibus similes, sed maiores et magis clavato-capitulatae. Epicutis contextu ixotrichdermico, hyphis subtilius composito (x 3–5 μm latis), cellulis terminalibus manifeste clavatis (apice x (4) 5,5–7 μm), sparsis cutis parum distincta pseudocollenchymatica; subcutis valde manifesta, typice pseudoparenchymatica hyphis composita pigmento membranario incrustato vivide tinctis brunneo-rufescenti vel aurantio-rufescenti. Fibulae adsunt. Habitat in phytocoenosis eliophilis (id est in silvis raris, caeduis vel in earum margine) subarboris coniferis (Piceis, Pinis) vel frondosis (Carpinis, Ostryis, Quercubus), gregarius at saepe solitarius.

• arrow_drop_downarrow_drop_upEnglish translation
  Pileus 30–40(–55) mm broad, fleshy, elastic, somewhat irregular, subhemispherical at first with involute margin, then convex, later quasi applanate, always with blunt umbo and involute then inflexed margin, sometimes weakly gibbous and with subsinuate margin. Cuticle uniform, glabrous, viscous, white, shiny almost as if covered with dew. Margin subpruinose when young and weakly sulcate. Colour uniform, cocoa-like, reddish-cocoa, brown-red, sometimes subpallescent at disc, almost yellow-ochre. Lamellae crowded, narrow (3–5 mm), rounded-adnexed, interspersed with subtruncate lamellulae, dry or slightly weeping with watery guttules when young, but never spotted, usually pale coloured, white then pale brownish ochre up to brown-clay coloured or reddish ochre, sometimes with greyish colours with minutely crenulate, pruinose, whitish edge. Stipe 30–50 × 7–10(–12) mm, sordid, subcylindrical, sometimes towards base somewhat attenuate, entirely fibrillose-striate, densely pruinose from apex to almost the base, solid to fistulose; uniformly white then discolouring brown. Cortina absent even in immature specimens. Context of pileus purely white, in stipe hardly browning at base. Smell subraphanoid in freshly collected specimens, raphanoid when cut; taste raphanoid slightly bitter. Spores (8) 8.5–10.5 (11) × 4.5–5.5 μm, elongate-amygdaloid, often with elongate apical papilla, smooth or punctate in ammonia, potassium and sodium hydroxide, with slight yellow tinge in microscope, dextrinoid. Basidia four-spored, 25–30 × 7–8 μm. Marginal cells (20) 30–45(–60) × 4–6 μm, subcylindrical to clavate-capitate with often enlarged apex, × 7–9 μm. Caulocystidia similar to marginal cystidia, but larger and strongly clavate-capitate. Epicutis an ixotrichoderm of delicate hyphae (3–5 μm wide), terminal elements distinctly clavate, (apex (4) 5–7 μm), but sparse; cutis indistinctly pseudocollenchymatical; subcutis very manifest of pseudoparenchymatical type, with vividly brown to reddish brown coloured encrusting pigment. Clamps present. Habitat in heliophilous phytocoenoses (open woodlands) under conifers (Pinus, Picea) or deciduous trees (Carpinus, Ostrya, Quercus), solitary or in groups.

Description

Description of Hebeloma theobrominum based on 41 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (20) 23–64 (65) mm diameter; shape often convex, occasionally umbonate, rarely broadly umbonate; characters occasionally pruinose, rarely spotting; margin characters usually smooth, occasionally involute, rarely wavy or reflexed; viscosity tacky when moist; colour variation usually unicolour, rarely two color; colour at centre occasionally brick or dark brick, rarely umber, clay-red, cinnamon, ochraceous, orange-brown or fawn.

  Lamellae: attachment often emarginate, occasionally adnexed or adnate; maximum depth 3–6 mm; number of complete lamellae 60–104; presence of tears often absent, occasionally visible with naked eye, rarely visible with x10 lens; white fimbriate edge occasionally weak, present or absent.

  Cortina presence: no.

  Stipe: (22) 30–66 (80) x 5–13 (17) {median} x 5–13 (17) {basal} mm; stipe Q 2.2–8.0; base shape often cylindrical, occasionally tapering, rarely clavate or bulbous; floccosity often pruinose, occasionally floccose, rarely fibrillose, floccose at apex, weakly floccose or none; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior often hollow, occasionally stuffed, rarely superior wick; stipe flesh discolouring usually no, rarely weak or yes; slenderness measure 1.3–12.8; smell often raphanoid, occasionally strongly raphanoid or cocoa, rarely weakly raphanoid; taste often bitter or raphanoid, occasionally weakly bitter or weakly raphanoid where recorded.

  Spore deposit colour: often brownish olive, occasionally umber.

  Exsiccata characters: occasionally pileus blackening or rich brown color, rarely dark, hard or stipe blackening.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, occasionally fusoid, rarely limoniform; colour in microscope occasionally very pale, brown, yellow pale or yellow brown, rarely brown pale; guttules usually yes, rarely no or weak. papilla often no, occasionally weak, rarely yes; Spore Code: O1 O2; P0 P1; D3 (D4).

  Basidia: 17–30 (33) x 5–8 (9) μm; ave. Q 3.1–4.0; spore arrangement 4 spored;

  Cheilocystidia: main shape usually clavate-lageniform or clavate-ventricose, occasionally cylindrical or ventricose, rarely lageniform, gently clavate, capitate, clavate or pyriform; special features observed occasionally septa, short or median thickening, rarely apical thickening, many collapsed in exsiccata, clamped septa, geniculate, mucronate, irregular, bifurcate or grotesque; cheilocystidia ratios: A/M = 1.33–1.69; A/B = 0.96–1.45; B/M = 0.94–1.61.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 175 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation variable; shape of trama elements beneath subcutis often cylindrical, occasionally ellipsoid, isodiametric, thickly sausage-shaped or spherical up to 13 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 110 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma theobrominum's preferred habitat appears to be coniferous woodland or deciduous woodland. Where only one possible associate was recorded, the most commonly recorded associate was Quercus (20.0%) but Pinus (20.0%), Fagus (16.0%), Helianthemum (12.0%), Picea (8.0%), Salix (8.0%), Tilia (4.0%), Betula (4.0%), Cedrus (4.0%) and Pseudotsuga (4.0%) were also recorded. In these cases the most commonly recorded families were Pinaceae (40.7%), Fagaceae (33.3%), Cistaceae (11.1%) and Salicaceae (7.4%). We have additional records where Abies (10.0%), Alnus (7.5%), Larix (7.5%), Ostrya (2.5%) and Corylus (2.5%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Pinaceae (42.5%), Fagaceae (32.5%), Betulaceae (17.5%), Cistaceae (7.5%) and Salicaceae (7.5%) The growth habit of our collections was occasionally scattered, solitary or gregarious and rarely caespitose or connate.

  According to our current collections, the species is predominantly found in Europe (90.2%) but also found in Temperate Asia (7.3%) and Tropical Asia (2.4%). On these continents, collections have 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. temperate broadleaf & mixed forests (60.0%) and mediterranean forests, woodlands & scrub (22.5%). 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 Southeast (Italy), the North (England, Denmark, Norway and Sweden), the Southwest (France and Spain), the Centre (Belgium, Poland and Hungary) and Eastern Europe (Estonia). Specimens have been collected from 39.2°N to 60.3°N.

  Within Temperate Asia all our records are from Caucasus (Karachay-Balkar).

  Within Tropical Asia all our records are from Indian Subcontinent (Pakistan).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma theobrominum is molecularly distinct in all loci tested apart from nucLSU (Eberhardt et al. 2013). The ITS of the type of H. theobrominum has been sequenced and clearly supports the species identification of our collections. Hebeloma theobrominum does form a well-bootstrap-supported monophyletic clade. The closest phylogenetic relatives of this taxon appear to be H. erumpens and H. griseopruinatum, both of which are associating with Cistaceae, and H. vesterholtii. There is little doubt based on the molecular results of (Eberhardt et al. 2013) that these species are all included in H. sect. Theobromina.

• arrow_drop_downarrow_drop_upCommentary
  The combination of almost smooth to very weakly ornamented and weakly but distinctly to very strongly dextrinoid spores, the hourglass (clavate-lageniform) shape of the cheilocystidia and the pruinose pileus all indicate H. sect. Theobromina. Hebeloma heobrominum can be macroscopically distinguished from other species of H. sect. Theobromina by means of its habitat and the richly coloured pileus, often described as red-brown or chocolate-brown. Microscopically, the weakly ornamented, narrow spores (max. 5.5 μm) with high Q (at least 1.8) together with the clavate-lageniform shaped cheilocystidia distinguish this species from other species of H. sect. Theobromina, except H. alboerumpens from which it is easily distinguished through the pileus colour and the habitat. Hebeloma theobrominum can be distinguished from the morphologically similar taxon H. vesterholtii, which also grows in calcareous places with Quercus, macroscopically by means of the pileus colour and microscopically by means of the higher spore Q value. Vesterholt (2005) had synonymized H. truncatum var. pruinosum with H. theobrominum. We (Eberhardt et al. 2013) have shown both morphologically and molecularly that these two species are distinct and that H. truncatum var. pruinosum is in fact synonymous with H. erumpens. Quadraccia (1987) introduced H. theobrominum as corresponding to H. firmum sensu Ricken (1915), non Persoon (1798) and H. truncatum sensu Lange (1938a) non Fries (1821). Schaeffer (1774) described the species Agaricus truncatus, which became the basionym for two totally different mushrooms from two distinct genera, namely Rhodocybe truncata (Schaeff.) Singer (1946) and Hebeloma truncatum (Schaeff.) Kummer (1871). It is generally accepted that the correct interpretation of Agaricus truncatus is R. truncata. Hence, Quadraccia described H. theobrominum as a new species to give a valid name to the species of Ricken and Lange and indeed many more modern authors including: Kühner & Romagnesi (1953), Favre (1960), Bruchet (1970) and Moser (1983). We are confident that Schaeffer’s description and icon (the holotype) does not represent a Hebeloma species. Note that Quadraccia’s H. theobrominum does not correspond to the species referred to as H. truncatum by Bon & Chevassut (1974), which has strongly ornamented spores with strongly loosening perispore.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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