Hebeloma celatum (Photo: H. J. Beker)

Taxonomy

Types: GERMANY: Baden-Württemberg, Teningen Unterwald NN, MTB7812/4 (48.124°N, 7.7797°E, alt. approx. 190 m a.s.l.) on calcareous soil and litter in deciduous woodland lakeside pathside under Carpinus sp. and Quercus sp., 19 Sep. 2010, H.J. Beker, L. Davies (Holotype. herbarium acc. no. BR 5020184119676, HJB13621).

• arrow_drop_downarrow_drop_upEtymology
  From celatus– hidden. For a long time we believed that Hebeloma celatum, H. erebium and H. quercetorum were all conspecific and this was backed up by our ITS sequencing. It was only when we began to generate sequences from other loci that we realized there may be more than one species hidden here and then by examining the morphological parameters on our database we finally started to realize that we could separate these taxa using morphological and biogeographical data. Hence we chose to name our new species here as ‘hidden’.

• arrow_drop_downarrow_drop_upDiagnosis
  Hebeloma celatum differs in its ITS sequence from all other congeners except for H. erebium and H. quercetorum, to which it is closely related, both phylogenetically and morphologically. The molecular separation from the latter two species is possible through RPB2, Tef1a, mitSSU V6 and V9. Morphologically, it differs from H. quercetorum in the by far larger number of clavate and clavate-ventricose cheilocystidia, which is correlated with the cheilocystidium ratio A/M > 1.25, and from H. erebium – which appears to be restricted to Northern Europe, north of 48° latitude – in the more robust stature, with stipe median diameter > 8 mm, and stipe base diameter > 13 mm.

Description

Description of Hebeloma celatum based on 127 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (23) 31–61 (77) mm diameter; shape often convex, occasionally umbonate or broadly umbonate, rarely strongly umbonate or weakly umbonate; characters occasionally spotting or hygrophanous, rarely rugulose; margin characters often smooth, rarely involute, eroded, scalloped or wavy; viscosity tacky when moist; colour variation often unicolour, occasionally two color; colour at centre occasionally dark pinkish buff, rarely ochraceous, umber, clay-buff, cinnamon, warm buff, yellowish brown, buff-yellow, dark brick or cream.

  Lamellae: attachment usually emarginate, rarely adnexed or decurrent tooth; maximum depth 3–11 mm; number of complete lamellae 56–78; presence of tears often absent, occasionally visible with naked eye, rarely visible with x10 lens; white fimbriate edge often present, occasionally weak.

  Cortina presence: no.

  Stipe: (24) 34–76 (110) x (4) 6–12 (16) {median} x (5) 8–20 (25) {basal} mm; stipe Q 2.8–12.8; base shape often clavate or bulbous, occasionally cylindrical, rarely subbulbous or tapering; floccosity occasionally floccose or pruinose, rarely fibrillose, pruinose at apex, velute, weakly floccose, none, floccose at apex or powdery; 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 or basal wick; stipe flesh discolouring often yes, occasionally no, rarely weak or very strongly; slenderness measure 1.7–19.3; smell often raphanoid, occasionally strongly raphanoid, rarely weakly raphanoid, cocoa or odourless; taste often mild or raphanoid, occasionally bitter, rarely weakly bitter or weakly raphanoid where recorded.

  Spore deposit colour: often brownish olive, occasionally umber.

  Exsiccata characters: occasionally fragile or pileus blackening, rarely lamellae blackening.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, usually limoniform, rarely fusoid; colour in microscope often yellow brown, occasionally brown, rarely yellow; guttules often yes, occasionally weak, rarely no. papilla often yes, occasionally weak, rarely very strongly; Spore Code: O3 (O4); P1 P2; D3 D4.

  Basidia: (23) 25–41 x 6–10 μm; ave. Q 3.2–4.4; spore arrangement 4 spored;

  Cheilocystidia: main shape ventricose, usually lageniform, often clavate-lageniform or clavate-ventricose or gently clavate, occasionally clavate-stipitate, clavate or cylindrical, rarely capitate or capitate-stipitate; special features observed occasionally septa, geniculate or bifurcate, rarely branching, clamped septa, irregular, apical thickening, short, sparse or yellow contents; cheilocystidia ratios: A/M = 1.06–1.73; A/B = 0.71–1.39; B/M = 1.35–1.80.

  Pleurocystidia: usually none seen, rarely seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 100 μm; ixocutis hyphae width up to 8 μm; ixocutis hyphae encrustation often no, occasionally yes; shape of trama elements beneath subcutis often ellipsoid, occasionally angular or thickly sausage-shaped up to 20 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 150 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma celatum's preferred habitat appears to be deciduous woodland with decomposed litter. Where only one possible associate was recorded, the most commonly recorded associate was Quercus (42.6%) but Fagus (19.7%), Pinus (9.8%), Carpinus (6.6%), Abies (4.9%), Populus (4.9%), Tilia (3.3%), Betula (3.3%), Corylus (1.6%), Dryas (1.6%) and Alnus (1.6%) were also recorded. In these cases the most commonly recorded families were Fagaceae (62.7%), Pinaceae (16.4%) and Betulaceae (11.9%). We have additional records where Cistus (4.5%), Castanea (2.7%), Picea (2.7%), Ostrya (2.7%) and Arbutus (1.8%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Fagaceae (72.3%), Betulaceae (28.6%), Pinaceae (25.0%) and Salicaceae (5.4%) The growth habit of our collections was often scattered, occasionally gregarious and rarely solitary, caespitose or connate.

  According to our current collections, the species is predominantly found in Europe (92.9%) but also found in Temperate Asia (7.1%). 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 (53.8%) and temperate broadleaf & mixed forests (35.3%), specifically including the ecoregions: Italian sclerophyllous and semi-deciduous forests (17.6%), European Atlantic mixed forests (10.1%), Appenine deciduous montane forests (10.1%) and Northeast Spain and Southern France Mediterranean forests (10.1%). 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 Southeast (Italy, North Macedonia and Bulgaria), the Southwest (Spain, France, Portugal and Italy), the Centre (Germany, Belgium, Poland and Slovakia) and the North (Norway, Denmark and Iceland). Specimens have been collected from 38.7°N to 69.4°N.

  Within Temperate Asia we have records from Western Asia (Cyprus and Turkey), Caucasus (Adygea) and China (Tibet).

• arrow_drop_downarrow_drop_upMolecular results
  This species can be recognized by all tested loci apart from ITS. With ITS, H. celatum cannot be differentiated from H. erebium and H. quercetorum. 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 celatum has a mixture of differently shaped cheilocystidia. This taxon has both ventricose or lageniform cheilocystidia that are mixed with cylindrical cheilocystidia and gently clavate cheilocystidia, wider at the apex and tapering below, as well as cheilocystidia that 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 belongs to either H. sects. Sinapizantia or Velutipes. (While it could be confused with taxa from H. sect. Denudata subsect. Echinospora, taxa of this latter section do not have lageniform or ventricose cheilocystidia.) With regard to H. sect. Sinapizantia, the lower number of lamellae and the less robust appearance rule it out of this section. The presence of ventricose cheilocystidia could cause confusion with H. sinapizans, but in addition to the characters mentioned above, other macroscopic differences include the occasional presence of tears and the occasional discolouration of the stipe and, microscopically, by the presence of gently clavate and clavate-lageniform cheilocystidia. Within H. sect. Velutipes, Hebeloma celatum is within the quercetorum-complex and hence is closely related, both phylogenetically and morphologically to H. erebium and H. quercetorum. Hebeloma erebium and H. quercetorum are confined respectively to Northern and Southern Europe; H. celatum, while exhibiting some preference for Southern Europe does also occur in Northern Europe. Hebeloma celatum can be differentiated from H. quercetorum through the much larger number of clavate or clavate-lageniform cheilocystidia which is reflected in the cheilocystidium ratio A/M always being larger than 1.25, while for H. quercetorum this ratio never exceeds 1.22. Within Northern Europe, this taxon can be distinguished from H. erebium as it generally has more robust basidiomes and, in particular, the stipe width at the median point usually exceeds 8 mm, while the width at the base usually exceeds 13 mm; neither of these widths are exceeded in basidiomes of H. erebium. With regard to H. aestivale, which is macroscopically very similar and which favours 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. celatum L = (52) 60–78 with average over 68. Microscopically, these two taxa are very easy to separate both on the cheilocystidia, which are quite different, and on the spores where H. aestivale has a strongly and constantly loosening perispore. It is worth noting that the isotype of H. quercetorum (K(M)20803) should actually be referred to this taxon and we have included this collection within our description of the species.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

Image gallery