Hebeloma islandicum (Photo: H. J. Beker)

Taxonomy

Types: ICELAND: West Fjords (65.7433°N, 23.1563°W, alt. approx. 295 m a.s.l.) on bare, calcareous soil in arctic shrubland under Salix herbacea, 28 Jul. 2005, H.J. Beker, M.L. Beker, det: H.J. Beker (Holotype. herbarium acc. no. BR 5020184116583, HJB11034).

• arrow_drop_downarrow_drop_upEtymology
  From islandicus–this taxon is, at this time, only known from Iceland.

• arrow_drop_downarrow_drop_upDiagnosis
  Hebeloma islandicum recalls in its habit H. alpinum. Microscopically, it shows a mix of clavate, clavate-lageniform and ventricose cystidia in combination with rather large spores on average greater than 11 μm long and 6 μm wide with distinctly to strongly dextrinoid (D3) spores, weakly ornamented (O2) and with only indistinctly loosening perispore (P0,P1). Molecularly, it shows an affinity with members of H. sect. Naviculospora, but is rather isolated within the genus. Only known from a single collection from subarctic Iceland.

Description

Description of Hebeloma islandicum based on 4 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (20) 24–34 (40) mm diameter; shape often convex or umbonate; characters often remains of universal veil; margin characters often involute or smooth; viscosity tacky when moist; colour variation two color; colour at centre yellowish brown.

  Lamellae: attachment emarginate; maximum depth up to 5 mm; number of complete lamellae 43–50; presence of tears visible with naked eye; white fimbriate edge present.

  Cortina presence: no.

  Stipe: (17) 19–22 (25) x 4 (6) {median} x (4) 5–6 (7) {basal} mm; stipe Q 3.4–5.5; base shape often clavate or cylindrical; floccosity floccose, often pruinose at apex; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior hollow; stipe flesh discolouring yes; slenderness measure 3.0–4.1; smell occasionally raphanoid or weakly raphanoid; taste often bitter or mild where recorded.

  Spore deposit colour: Not recorded.

  Exsiccata characters: Not recorded.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, often limoniform; colour in microscope often yellow brown, occasionally brown pale, yellow or yellow pale; guttules variable. papilla yes; Spore Code: (O1) O2; P0 P1; D2 D3.

  Basidia: 28–39 (40) x 6–9 μm; ave. Q 3.7–4.9; spore arrangement 4 spored;

  Cheilocystidia: main shape clavate-stipitate or clavate-lageniform or clavate-ventricose, often capitate-stipitate or ventricose, occasionally clavate, gently clavate, cylindrical, lageniform or pyriform; special features observed often irregular, septa, clamped septa or geniculate, occasionally branching, conglutinate, distorted, grotesque or rostrate; cheilocystidia ratios: A/M = 1.63–1.98; A/B = 1.04–1.85; B/M = 1.05–1.73.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 120 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation often yes, occasionally no; shape of trama elements beneath subcutis often ellipsoid, isodiametric or thickly sausage-shaped, occasionally oblong or thinly sausage-shaped up to 20 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 140 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma islandicum's preferred habitat appears to be arctic shrubland, arctic tundra snowbed or alpine tundra snowbed with bare, calcareous soil, soil or acidic soil. Across our collections, Hebeloma islandicum has only been recorded as associating with Salix (family Salicaceae). The growth habit of our collections was scattered.

  According to our current data, the species is found on multiple continents with collections found in Europe (75.0%) and Northern America (25.0%). 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. tundra (50.0%), boreal forests/taiga (25.0%) and unknown biome (25.0%), specifically including the ecoregions: Scandinavian Montane Birch forest and grasslands (50.0%), Iceland boreal birch forests and alpine tundra (25.0%) and Unknown region (25.0%). From collector information, it appears collections have been found in the 5.1 Wetlands (inland) – Permanent rivers/streams/creeks (includes waterfalls) (50.0%), 4.1 Grassland – Tundra (25.0%) and 5.11 Wetlands (inland) – Alpine wetlands (inc. temporary waters from snowmelt) (25.0%) 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 all our records are from the North (Norway and Iceland). Specimens have been collected from 60.3°N to 65.7°N.

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

• arrow_drop_downarrow_drop_upMolecular results
  The sequences of this collection are clearly distinct from all other European Hebeloma spp. As pointed out under H. sect. Naviculospora the molecular association of this species with the section is unclear. Both, ITS and RPB2 support the inclusion of H. islandicum in H. sect. Naviculospora, but without bootstrap support, whereas other loci do not.

• arrow_drop_downarrow_drop_upCommentary
  Hebeloma islandicum is currently only known from one remote location in the West Fjords of Iceland. It is an unusual Hebeloma that does not appear to fit comfortably in any of our sections. For the moment we have included it in H. sect. Naviculospora, but we are aware that future authors, with more collections of this taxon and also more species from other parts of the world, may change this placement. Its stature is reminiscent of H. alpinum but the cheilocystidia are more typical of H. sect. Denudata subsect. Clepsydroida. The spores of H. islandicum are only weakly ornamented (O2) and the perispore is not distinctly and consistently loosening in many spores (P0,P1). The spores are on average 11.8 × 6.6 μm which make them amongst the biggest from H. sects. Scabrispora and Naviculospora. If one mistakenly tried to key this species out in the key for H. sect. Denudata, the clavate-lageniform cheilocystidia and the large number of rather strongly dextrinoid spores (D3) would lead to subsect. Clepsydroida, but there is no species in this subsection with spores only weakly ornamented, O2. Because of the possible confusion with H. sect. Denudata, we include Hebeloma islandicum in both the key for H. sect. Denudata and the key to H. sects. Duracinus, Myxocybe, Naviculospora, Scabrispora and Syrjense.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

Image gallery