Hebeloma salicicola (Photo: H. J. Beker)

Taxonomy

Types: BELGIUM: West Flanders, De Panne (51.0879°N, 2.5757°E, alt. approx. 5 m a.s.l.) on sandy soil in dune under Salix repens, 12 Oct. 2009, H.J. Beker, L. Davies (Holotype. herbarium acc. no. BR BR-MYCO 173977-56 (holotype), C C-F-90151 (isotype), HJB13302).

• arrow_drop_downarrow_drop_upEtymology
  From Salix– and –cola meaning dweller, being exclusively mycorrhizal with Salicaceae.

• arrow_drop_downarrow_drop_upDiagnosis
  Hebeloma salicicola is a member of H. subsect. Denudata [H. subsect. Crustuliniformia] based on cheilocystidium shape, though the cystidia can be rather broad at the base. Macroscopically it is similar to H. vaccinum, but in contrast to H. vaccinum, mature specimens nearly always have a two-coloured pileus with a darker centre. Microscopically H. salicicola differs from other members of its subsection by a combination of characters, i.e. its small stature, the low number of full length lamellae (less than 50), the rather strong dextrinoidity (D2,D3) and ornamentation of the spores (O2,O3), which are on average longer than 11 µm.

Description

Description of Hebeloma salicicola based on 57 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (9) 12–40 (48) mm diameter; shape often convex, occasionally umbonate, rarely broadly umbonate or strongly umbonate; characters rarely hygrophanous or remains of universal veil; margin characters often smooth, rarely crenulate, scalloped, involute or sulcate; viscosity tacky when moist; colour variation often two color, occasionally unicolour; colour at centre occasionally yellowish brown or ochraceous, rarely clay-buff, brownish olive, umber, dark pinkish buff, sepia, dark brick, cinnamon, greyish brown or warm buff.

  Lamellae: attachment usually emarginate, rarely adnate, free or adnexed; maximum depth 2–9 mm; number of complete lamellae 28–55; presence of tears occasionally visible with naked eye, absent or visible with x10 lens; white fimbriate edge usually present, occasionally weak, rarely very strong.

  Cortina presence: no.

  Stipe: (5) 14–44 (56) x (1) 2–6 (15) {median} x (1) 2–8 (15) {basal} mm; stipe Q 2.3–12.0; base shape often cylindrical, occasionally clavate, sand bulb or tapering, rarely bulbous; floccosity occasionally pruinose or pruinose at apex, rarely fibrillose, floccose, floccose at apex, velute or weakly floccose; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior often stuffed or hollow, rarely superior wick; stipe flesh discolouring variable occasionally weak; slenderness measure 2.0–23.6; smell often raphanoid, occasionally cocoa or odourless, rarely weakly raphanoid or earthy; taste often mild, occasionally weakly bitter, bitter, raphanoid or weakly raphanoid where recorded.

  Spore deposit colour: occasionally brownish olive or umber, rarely sepia or greyish brown.

  Exsiccata characters: occasionally lamellae blackening, rarely dark or shiny.

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

  Basidia: (22) 23–37 (38) x (5) 6–9 (10) μm; ave. Q 3.0–4.1; spore arrangement 4 spored;

  Cheilocystidia: main shape clavate-stipitate, often clavate-lageniform or clavate-ventricose, occasionally capitate-stipitate, rarely capitate, gently clavate, spathulate or utriform; special features observed occasionally apical thickening, rarely bifurcate, many collapsed in exsiccata or septa; cheilocystidia ratios: A/M = 1.77–2.63; A/B = 1.38–2.82; B/M = 0.94–1.32.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 150 μm; ixocutis hyphae width up to 10 μm; ixocutis hyphae encrustation usually yes, occasionally no; shape of trama elements beneath subcutis often thickly sausage-shaped, occasionally ellipsoid, thinly sausage-shaped, cylindrical, isodiametric, oblong, ovate or polygonal up to 16 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 85 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma salicicola's preferred habitat appears to be coastal dune or dune with sandy soil or calcareous, sandy soil. Where only one possible associate was recorded, the most commonly recorded associate was Salix (95.5%) but Populus (4.5%) were also recorded. In these cases the most commonly recorded family was Salicaceae (97.8%). We have additional records where Betula (5.9%), Pinus (2.0%), Cedrus (2.0%), Abies (2.0%), Picea (2.0%), Alnus (2.0%) and Corylus (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 Salicaceae (98.0%), Betulaceae (7.8%) and Pinaceae (5.9%) The growth habit of our collections was usually scattered and rarely solitary or gregarious.

  According to our current collections, the species is predominantly found in Europe (96.5%) but also found in Temperate Asia (1.8%) and Northern America (1.8%). On these continents, collections have been found only in the European Atlantic mixed forests WWF ecoregion 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 biome). From collector information, it appears collections have been found only in the 13.3 Coastal Sand Dunes 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 Centre (Belgium, Netherlands, Poland and Germany), the North (Wales, Svalbard, Denmark, Finland, Scotland and Norway), the Southwest (Spain and France), Eastern Europe (Estonia) and the Southeast (Italy). Specimens have been collected from 40.4°N to 78.9°N.

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

  Within Northern America all our records are from Subarctic America (Alaska).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma salicicola is monophyletic in the ML trees resulting from the analysis of five or six loci concatenated and can be identified based on ITS, RPB2 and Tef1a data. In single locus analyses of these loci and with MCM7, H. salicicola forms monophyletic clades; the MCM7 sequences obtained for this species are, however, rather diverse (Eberhardt et al. 2015a). We are not aware of any ITS sequences from outside Europe that are likely to belong to this species.

• arrow_drop_downarrow_drop_upCommentary
  Given the shape of its cheilocystidia, Hebeloma salicicola clearly belongs to H. sect. Crustuliniformia and, although its cheilocystidia are perhaps more swollen in their lower half than most other species of H. subsect. Crustuliniformia, this taxon still falls within the subsection parameters. This species most likely corresponds to ICG14 of Aanen & Kuyper (1999). In the key to this subsection we key H. salicicola out in both subkeys. It can be distinguished from other arctic/alpine species of this subsection through the number of lamellae, less than 60, and the spores more ornamented or more dextrinoid than H. aurantioumbrinum, H. alpinum, H. louiseae, H. minus, H. pallidolabiatum and H. perexiguum and usually without as strong a papilla as H. alpinum. It can be separated from other lowland species in this section through the number of full length lamellae, between 30 and 50, the spore length, greater than 11 μm, the smallish stature and the dextrinoidity of the spores. In the past this species has probably been confused with H. vaccinum (particularly as both may grow together in dune slacks and have a similar macroscopic appearance) and perhaps H. pusillum in dunes and lowland areas and with H. minus in alpine and arctic habitats. Originally, we referred to this taxon as Hebeloma cephalotum nom. prov., as it matched closely with the description of Hebeloma vaccinum var. cephalotum in Enderle (2004). However, we have examined the holotype of this species (M M-0155166) and it appears to be a mixed collection. All the fragments we have examined, morphologically and molecularly, are of Hebeloma pusillum. However, the species described in the protologue fits far better with the taxon we have described here, Hebeloma salicicola. In an attempt to resolve this, we also examined an isotype (C C43996), but this collection, based on both molecular and morphological study, is H. vaccinum. We do believe that the material of H. vaccinum var. cephalotum originally studied by J. Vesterholt corresponded to H. salicicola, however, given the mixed nature of both the holotype and the isotype of H. vaccinum var. cephalotum, we concluded that it is safer to describe this taxon as new (Eberhardt et al. 2015a).

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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