Hebeloma geminatum (Photo: J. Vesterholt)

Taxonomy

Types: DENMARK: NWJ, Nystrup Klitplantage, S of Kridtstien UTM MJ6920 (approx. 57.0267°N, 8.4906°E, alt. approx. 15 m a.s.l.) on calcareous soil in woodland plantation under Abies sp., 20 Oct. 1996, J. Vesterholt (Holotype. herbarium acc. no. C C-F-90152 (holotype), BR MYCO 173983-62 (isotype), HJB10833).

• arrow_drop_downarrow_drop_upEtymology
  From the base geminus– a double or twin, to emphasise that this is one of two taxa that can be differentiated molecularly and biologically but for which we have found no unambiguous morphological character to separate them.

• arrow_drop_downarrow_drop_upDiagnosis
  Hebeloma geminatum with primarily capitate-, clavate- or spathulate-stipitate cheilocystidia belongs to H. subsect. Denudata [H. subsect. Crustuliniformia]. It can be distinguished from other taxa of the section by its average number of lamellae, which is ≥ 60, its spores, which are on average between 6 [this should read 5.4] and 6.4 μm wide and < 10.75 μm long, and the cheilocystidia apex, which is always on average > 8 μm and often > 9 μm. The species is morphologically most similar to H. aanenii from which it can be distinguished by comparison of the sequence of the internal transcribed spacer region of the nuclear ribosomal RNA genes.

Description

Description of Hebeloma geminatum based on 74 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (16) 24–85 (120) mm diameter; shape often convex, rarely broadly umbonate, umbonate or strongly umbonate; characters rarely spotting, hygrophanous or rugulose; margin characters occasionally involute or smooth, rarely crenulate, scalloped, flexuous, reflexed, ribbed, sulcate or wavy; viscosity tacky when moist; colour variation usually unicolour, rarely two color; colour at centre occasionally pale cream, cream or pale yellow, rarely ochraceous or pale pinkish buff.

  Lamellae: attachment often emarginate, occasionally adnate, rarely adnexed; maximum depth 2–8 mm; number of complete lamellae 60–100; presence of tears usually visible with naked eye, rarely visible with x10 lens; white fimbriate edge often present, occasionally very strong.

  Cortina presence: no.

  Stipe: (15) 28–79 (110) x (5) 6–12 (22) {median} x (5) 7–14 (16) {basal} mm; stipe Q 2.1–10.6; base shape often clavate or cylindrical, rarely tapering, bulbous or subbulbous; floccosity usually floccose, occasionally pruinose, rarely fibrillose or pruinose at apex; rooting no; thick rhizoids at base usually absent, rarely present;

  Context: Texture firm; stipe interior often hollow or stuffed, rarely superior wick; stipe flesh discolouring often no, occasionally yes, rarely weak; slenderness measure 1.0–17.8; smell often raphanoid, rarely odourless, strongly raphanoid, weakly raphanoid or farinaceous; taste often mild or raphanoid, occasionally weakly bitter where recorded.

  Spore deposit colour: often brownish olive, rarely 5d5 or greyish brown.

  Exsiccata characters: occasionally pale, rarely fragile.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, rarely fusoid; colour in microscope often yellow brown, occasionally brown or brown yellow, rarely grey yellow, yellow or yellow pale; guttules usually yes, occasionally no. papilla often no, occasionally weak; Spore Code: O2 O3; (P0) P1; D0 D1.

  Basidia: 21–37 x (5) 6–9 μm; ave. Q 3.3–4.3; spore arrangement 4 spored;

  Cheilocystidia: main shape clavate-stipitate, occasionally capitate-stipitate, spathulate-stipitate or clavate-lageniform or clavate-ventricose, rarely gently clavate or clavate; special features observed occasionally septa or sinuate, rarely conglutinate, wavy, bifurcate, spathulate, apical thickening, median thickening or subcapitate; cheilocystidia ratios: A/M = 1.76–2.57; A/B = 1.68–3.00; B/M = 0.77–1.19.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 200 μm; ixocutis hyphae width up to 8 μm; ixocutis hyphae encrustation variable; shape of trama elements beneath subcutis often ellipsoid, thickly sausage-shaped or cylindrical, occasionally thinly sausage-shaped up to 16 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
  Where only one possible associate was recorded, the most commonly recorded associate was Betula (26.5%) but Salix (17.6%), Pinus (14.7%), Fagus (8.8%), Dryas (8.8%), Picea (8.8%), Populus (5.9%), Abies (2.9%), Tilia (2.9%) and Helianthemum (2.9%) were also recorded. In these cases the most commonly recorded families were Betulaceae (26.3%), Pinaceae (26.3%), Salicaceae (23.7%), Rosaceae (10.5%) and Fagaceae (7.9%). We have additional records where Quercus (4.8%), Corylus (1.6%), Alnus (1.6%), Larix (1.6%) and Carpinus (1.6%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Betulaceae (46.8%), Salicaceae (38.7%), Pinaceae (37.1%), Fagaceae (12.9%) and Rosaceae (6.5%) The growth habit of our collections was often scattered, occasionally solitary and rarely gregarious or caespitose.

  According to our current collections, the species is predominantly found in Europe (95.8%) but also found in Northern America (4.2%). 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. temperate broadleaf & mixed forests (54.3%), boreal forests/taiga (15.7%) and unknown biome (14.3%), specifically including the ecoregions: European Atlantic mixed forests (17.1%), Unknown region (14.3%) and Scandinavian and Russian taiga (11.4%). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (42.1%), 17.1 Quarry (17.5%), 14.5 Urban Areas (10.5%) and 1.1 Forest – Boreal (10.5%) 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 North (Norway, England, Denmark, Sweden, Iceland and Finland), the Centre (Belgium, Poland, Germany, Netherlands and Switzerland), the Southwest (France and Spain), Eastern Europe (Estonia and Lithuania) and the Southeast (Italy). Specimens have been collected from 42.4°N to 70.2°N.

  Within Northern America all our records are from Western Canada (Alberta).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma geminatum is not monophyletic in the result of the five-locus result, but it is when using MCM7 as one of the loci concatenated. Molecularly, H. geminatum is very close to H. alpinum and only the V9 locus separates the two species. Hebeloma alpinum lacks an indel present in H. geminatum and some other members of H. subsect. Crustuliniformia. In fact, there is only a single bp difference between some H. aanenii and H. geminatum V9 sequences, but all other loci, including the ITS, can separate these two taxa. Apart from the inclusion of a deviant member of H. alpinum (HJB11051) and the exclusion of an untypical, but cited H. geminatum collection (HJB11545), H. geminatum forms a monophylum in analyses combining several loci including V9 (Eberhardt et al. 2015a). Based on ITS alone, H. geminatum cannot be distinguished from H. alpinum and other species of the alpinum-complex including also H. aanenii, H. eburneum, and possibly H. minus and H. pallidolabiatum; Eberhardt et al. 2015a).

• arrow_drop_downarrow_drop_upCommentary
  Given the shape of its cheilocystidia, Hebeloma geminatum clearly belongs to H. subsect. Crustuliniformia. This species most likely corresponds to ICG1 of Aanen & Kuyper (1999). Hebeloma geminatum is a constituent of the crustuliniforme-complex. It is likely that many collections of this species have been recorded under the name H. crustuliniforme and exist worldwide in herbaria under this name. It is similar to H. crustuliniforme, H. eburneum, H. alpinum and H. aanenii. But its spores, on average normally less than 11 μm long and less than 6 μm wide (rarely longer or wider) distinguish it from the first three species. It can be distinguished from other members of its subsection by the number of complete lamellae, which is always at least 60. Until now, we have found no consistent morphological character to separate H. aanenii and H. geminatum. However, we can often separate these two taxa through the use of a combination of characters, although none appears foolproof. The cheilocystidium average apex width for H. geminatum is usually larger than that for H. aanenii. From our records, if the average width of the apex of the cheilocystidium is more than 9 μm, then the collection is almost certainly H. geminatum. However, the average apex width can be as small as 8 μm and widths in this interval between 8 μm and 9 μm can be from either taxon. This is illustrated in the scatter diagram.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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