Hebeloma pubescens (Photo: H. J. Beker)

Taxonomy

Types: SVALBARD: Ny Alesund (78.9211°N, 11.9304°E, alt. approx. 30 m a.s.l.) on soil in arctic tundra pastureland under Salix polaris, 16 Aug. 2007, H.J. Beker, M.L. Beker (Holotype. herbarium acc. no. BR5020184127626, HJB12008).

• arrow_drop_downarrow_drop_upEtymology
  From pubescens– downy with short soft hairs. This species is unusual (but not unique) in having a tomentose pileus; the name is to emphasise this character.

• arrow_drop_downarrow_drop_upDiagnosis
  Hebeloma pubescens has a persisting cortina and lageniform or ventricose cheilocystidia and is, therefore, a member of H. section Hebeloma. Within this section, it can be differentiated through a combination of the arctic habitat, the macroscopic features, the number of full length lamellae (L < 30) and, importantly, the tomentose pileus, and microscopically through the large, indextrinoid, primarily ellipsoid spores.

Description

Description of Hebeloma pubescens based on 12 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (10) 11–21 (24) mm diameter; shape occasionally convex, umbonate, papillate or broadly umbonate; characters occasionally remains of universal veil or tomentose; margin characters usually smooth, occasionally involute; viscosity tacky when moist; colour variation often unicolour or two color; colour at centre occasionally umber, greyish brown, yellowish brown, brownish olive or sepia.

  Lamellae: attachment often emarginate, occasionally adnate; maximum depth 2–5 mm; number of complete lamellae 25–32; presence of tears absent; white fimbriate edge often weak, occasionally present or absent.

  Cortina presence: yes.

  Stipe: (11) 16–35 (46) x 2–3 (4) {median} x 2–3 (4) {basal} mm; stipe Q 3.7–11.5; base shape cylindrical; floccosity usually fibrillose, occasionally pruinose at apex; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior often hollow, occasionally stuffed; stipe flesh discolouring often yes, occasionally no; slenderness measure 4.9–21.9; smell often raphanoid, occasionally strongly raphanoid, rarely odourless or weakly raphanoid; taste often mild, occasionally bitter where recorded.

  Spore deposit colour: often brownish olive or yellowish brown.

  Exsiccata characters: Not recorded.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape ellipsoid, occasionally ovoid; colour in microscope often brown pale, occasionally brown yellow, yellow or yellow pale; guttules variable often weak. papilla no; Spore Code: O1 (O2); P0; D0 (D1).

  Basidia: 24–36 (37) x 6–10 μm; ave. Q 3.4–4.4; spore arrangement 4 spored;

  Cheilocystidia: main shape lageniform or ventricose; special features observed often basal thickening or septa, occasionally median thickening; cheilocystidia ratios: A/M = 1.02–1.10; A/B = 0.51–0.73; B/M = 1.52–2.10.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 100 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation yes; shape of trama elements beneath subcutis isodiametric, often thickly sausage-shaped up to 15 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 80 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma pubescens's preferred habitat appears to be arctic tundra or arctic tundra pastureland. Where only one possible associate was recorded, that associate has always been Salix (family Salicaceae). We have additional records where Dryas and Kobresia were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Salicaceae (100.0%), Rosaceae (16.7%) and Cyperaceae (8.3%) The growth habit of our collections was usually scattered and rarely solitary.

  According to our current data, the species is found on multiple continents with collections found in Europe (41.7%), Northern America (41.7%) and Temperate Asia (16.7%). 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 (83.3%) and unknown biome (16.7%), specifically including the ecoregions: Russian Arctic desert (41.7%), Kalaallit Nunaat Arctic steppe (33.3%) and Unknown region (16.7%). From collector information, it appears collections have been found only in the 4.1 Grassland – Tundra 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 all our records are from the North (Svalbard). Specimens have been collected from 78.2°N to 78.9°N.

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

  Within Temperate Asia all our records are from Russian Far East (Chukotka).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma pubescens receives high bootstrap support in the result of the five-locus analysis, as well as good support in the single locus results of RPB2 and Tef1a. In the results from mitochondrial loci and ITS, H. pubescens is included in the clade around H. dunense and H. mesophaeum, for which it would most likely be mistaken when using ITS for species identification.

• arrow_drop_downarrow_drop_upCommentary
  With the persistent presence of a cortina and the lageniform or ventricose cheilocystidia, this taxon clearly belongs in H. section Hebeloma. Within this section, it can be differentiated through a combination f macroscopic features, the number of full length lamellae (L < 30) and, importantly, the tomentose pileus, and, microscopically, through the large, primarily ellipsoid spores. The persistent tomentum on the pileus is an unusual character within the genus Hebeloma, and something we have only encountered before within H. sect. Sacchariolentia; indeed as happens within the species of that section, such as H. odoratissimum, as the pileus dries it breaks up into small squamules. Microscopically this taxon has ellipsoid spores similar to those of H. mesophaeum, with hardly any ornamentation, but larger than those of H. mesophaeum. Were it not for the macroscopic characters, morphologically this taxon might be confused with H. marginatulum. In our first studies of these collections we did in fact key these collections out on the database to H. marginatulum, but it was clear from the molecular sequences that it could not be this taxon. To date we only have three collections from Svalbard and so it is difficult to be certain about the species delimitation of this taxon.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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