Hebeloma odoratissimum (Photo: J. Vesterholt)

Taxonomy

Basionym:
Agaricus odoratissimus Britzelm., Hym. Südbayern 8: 8 (1891)

Types: Britzelmayr, Hym. Südbayern 8: 55 (1891) fig. 312, lectotype (icon) designated by Beker et al., Hebeloma (Fr.) P. Kumm.: (2016) page 524 (MBT203471) BELGIUM: Limburg, De rooten (51.0146°N, 5.3521°E, alt. approx. 50 m a.s.l.) on litter in deciduous slagheap bog under Betula sp. and Salix sp., 26 Oct. 2007, M. Driesen (Epitype. herbarium acc. no. BR 5020184121440, HJB12149). Epitype designated by Beker et al., Hebeloma (Fr.) P. Kumm.: (2016) page 524 (MBT203472).

• arrow_drop_downarrow_drop_upType notes
  The lectotype is from Britzelmayer, Hym. Südbayern 8: 8 fig. 312 (1891) [on its own on a page and not the drawing labelled F. 312 adjacent to drawing F. 313.

Heterotypic synonyms:

• Hebeloma hetieri Boud., Bulletin trimestriel de la Société Mycologique de France 33: 8 (1917)
• Hebeloma sacchariolens var. tomentosum M.M. Moser, Zeitschrift fuer Pilzkunde 36 (1-2): 71 (1970)
• Hebeloma tomentosum (M.M. Moser) Gröger & Zschiesch., Z. Mykol. 47 (2): 204 (1981)

• arrow_drop_downarrow_drop_upEtymology
  From odoratus– fragrant, perfumed, presumably to emphasise the intense aromatic odour of this fungus.

• arrow_drop_downarrow_drop_upOriginal diagnosis
  A. (Heb.) odoratissimus, n. sp., F. 312 (allein stehend, nicht neben F. 313(: Sp. 15 : 7,8; L. z. e. e. isabellfarben, dann zimmtfarben rotbraun; H. u. St. gelblich, dann gelbl. rotbraun bis dunkelrotbraun, die Oberfläche des Hutes sich nach und nach in kleine Fasern u. Schüppchen auflösend; Fl. wie der St. nach oben heller, nach unten dunkler rotlich braunlich von s. starkem Gewürzhaftem G., s. gebrechlich; Herbst, einzeln u. gesellschaftlich, schattige Grasplätze, A.

• arrow_drop_downarrow_drop_upEnglish translation
  Agaricus (Hebeloma) odoratissimus, new sp., F. 312 (solitary, not beside F. 313): Spores 15 × 7–8 μm; lamellae fairly distant to distant, narrow, Isabella-coloured, then cinnamon to reddish brown. Pileus and stipe yellowish, then yellowish reddish brown to dark red-brown, pileus surface progressively breaking up and dissolving into small fibrils and squamules; context like the stipe paler in upper part, darker reddish brown in lower part, with an intense aromatic odour, very fragile; autumn, solitary or in groups, in shady grassy spots. Common.

Description

Description of Hebeloma odoratissimum based on 27 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (10) 15–58 (80) mm diameter; shape often convex, occasionally umbonate or broadly umbonate; characters usually tomentose, often rimulose, occasionally squamulose, rarely granulose, remains of universal veil or scaly; margin characters usually smooth, occasionally involute or eroded; viscosity tacky when moist; colour variation usually unicolour, rarely two color; colour at centre occasionally yellowish brown, pale cream or clay-buff, rarely dark pinkish buff, honey, warm buff, ochraceous, cream, cinnamon or pinkish buff.

  Lamellae: attachment usually emarginate, rarely adnate or free; maximum depth 2–10 mm; number of complete lamellae 28–47; presence of tears absent; white fimbriate edge often absent, occasionally weak.

  Cortina presence: no.

  Stipe: (22) 29–68 (90) x (2) 3–8 (12) {median} x (2) 3–8 (12) {basal} mm; stipe Q 4.3–14.4; base shape often cylindrical, occasionally tapering or clavate, rarely bulbous; floccosity often fibrillose, occasionally pruinose or pruinose at apex; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior often hollow or stuffed; stipe flesh discolouring often yes, occasionally weak, rarely no; slenderness measure 4.8–25.4; smell sacchariolentia, often sweet, rarely fruit; taste bitter where recorded.

  Spore deposit colour: often brownish olive, occasionally sepia or umber.

  Exsiccata characters: often lamellae blackening, occasionally dark, pileus cracking or stipe blackening, rarely pileus blackening.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, usually limoniform; colour in microscope often brown, rarely brown pale or yellow brown; guttules often yes, occasionally no, rarely weak. papilla often very strongly, occasionally yes, rarely weak; Spore Code: O3 O4; P2 P3; D3 D4.

  Basidia: (25) 29–49 (50) x 7–10 μm; ave. Q 3.6–5.2; spore arrangement 4 spored;

  Cheilocystidia: main shape often cylindrical or gently clavate, occasionally balloon-shaped, clavate, filiform or clavate-lageniform or clavate-ventricose, rarely ventricose, lageniform or utriform; special features observed often septa or short, occasionally clamped septa or irregular, rarely median thickening, bifurcate, many collapsed in exsiccata or rostrate; cheilocystidia ratios: A/M = 0.98–1.47; A/B = 1.08–2.04; B/M = 0.65–1.07.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 70 μm; ixocutis hyphae width up to 12 μm; ixocutis hyphae encrustation variable; shape of trama elements beneath subcutis often ellipsoid, occasionally cylindrical, oblong or thickly sausage-shaped up to 25 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 70 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma odoratissimum's preferred habitat appears to be mixed woodland with grassy soil or bare soil. Where only one possible associate was recorded, the most commonly recorded associate was Salix (61.5%) but Populus (15.4%), Fagus (7.7%), Alnus (7.7%) and Quercus (7.7%) were also recorded. In these cases the most commonly recorded families were Salicaceae (83.3%), Betulaceae (8.3%) and Fagaceae (8.3%). We have additional records where Betula (13.6%), Corylus (4.5%), Castanea (4.5%), Abies (4.5%) and Picea (4.5%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Salicaceae (68.2%), Betulaceae (27.3%) and Fagaceae (13.6%) The growth habit of our collections was occasionally scattered, solitary or gregarious and rarely caespitose.

  According to our current collections, the species is found only in Europe. On the continent, 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. temperate broadleaf & mixed forests (72.0%) and temperate conifer forests (16.0%), specifically including the ecoregions: Western European broadleaf forests (24.0%), European Atlantic mixed forests (20.0%) and Alps conifer and mixed forests (16.0%). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (66.7%) and 17.1 Quarry (20.0%) IUCN habitats 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 (France and Spain), the North (England, Denmark and Norway), the Centre (Belgium, Germany, Poland and Switzerland) and the Southeast (Italy). Specimens have been collected from 41.8°N to 59.2°N.

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma odoratissimum is well distinct and forms well supported monophyletic clades in phylogenetic analyses of all loci tested. It can be identified with any one of ITS, V6, or V9; at this point we have only two RPB2 and Tef1a sequences each, but they do form well supported clades, too. We obtained the ITS from the type of H. sacchariolens var. tomentosum which is included in the clade of H. odoratissimum, thus supporting the synonymization. The closest relatives of H. odoratissimum, in phylogenetic terms, are probably H. sacchariolens and H. nauseosum. To date no ITS sequences from outside Europe have been published that are likely to belong to this species.

• arrow_drop_downarrow_drop_upCommentary
  The smell associated with Hebeloma odoratissimum immediately places it in H. sect. Sacchariolentia. The spore width, on average at least 7.5 μm, means it can only be H. nauseosum or H. odoratissimum. This taxon can be readily separated from H. nauseosum through the nature of the pileus. Hebeloma odoratissimum has a tomentose or velutinate pileus that often cracks into small scales, giving a squamulose look to the pileus, and a thin ixocutis of at most 70 μm thickness. Hebeloma nauseosum, on the other hand, has a smooth pileus, at most slightly velutinate at the margin, and with an ixocutis of 100–120 μm thickness. Unravelling the species described by Britzelmayr is never easy. However, in this case there is little doubt as to the identity of his species. In the protologue, Britzelmayr specifically mentions the large spores, giving a size and drawing the distinctive limoniform shape, the fairly distant lamellae, the colours including the discolouring with age and the intense odour, but most importantly he describes the pileus surface that gradually breaks up and dissolves into small fibrils and squamules. His drawing also shows this character of this taxon. In the plate that is selected here as lectotype, one of the basidiomes has a pileus colour that is a little darker than usual, but the other basidiomes in his drawing resemble quite well this taxon. We have searched extensively for any original material, but we failed to locate any. Nonetheless, with his diagnosis and the plate which he mentions in the protologue, we are satisfied that this taxon is synonymous with both H. hetieri and H. tomentosum. In the case of the latter we have examined the holotype material and, indeed, included it here within our overall description of this species; we have been unable to locate any original material of H. hetieri. Boudier, in his description of H. hetieri, also describes the pileus breaking up into squamules and becoming densely granulose as well as the colours, large spores and smell. (Boudier does give a spore size of 20–21 × 8–10 μm, but his spore sizes are quite often suspect (see van Brummelen 1969); no European Hebeloma that we have ever seen has spores of this size. Again, there can be no doubt that this description represents the same taxon. When examining material of this taxon, particularly old material, locating cheilocystidia can be very difficult. They are sparse and small and when collapsed in old material may be very difficult to separate from basidioles. In our experience, it is often better with such material to begin by searching near the apex of the stipe for caulocystidia. Whereas they too may have collapsed, the absence of basidioles usually makes them easier to locate. Once having established the shape of cystidia that are present, an examination of the lamella edge may be more fruitful.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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