Hebeloma aurantioumbrinum (Photo: H. J. Beker)

Taxonomy

Types: SVALBARD: Knudsenheia (78.9373°N, 11.8425°E, alt. approx. 10 m a.s.l.) on soil in arctic tundra pastureland under Salix polaris, 19 Aug. 2007, H.J. Beker, M.L. Beker (Holotype. herbarium acc. no. BR BR-MYCO 173985-64 (holotype), C C-F- 90148 (isotype), HJB12058).

• arrow_drop_downarrow_drop_upEtymology
  From aurantius– orange and umbrinus– umber.

• arrow_drop_downarrow_drop_upDiagnosis
  Hebeloma aurantioumbrinum possesses the cheilocystidia typical of H. subsect. Denudata [H. subsect. Crustuliniformia]. It is a species typically occurring in alpine or arctic habitats where it can be recognized by the combination of an average spore width of less than 7 µm and an average cheilocystidium apex width of less than 8.5 µm. Outside these habitats it can be differentiated from other small species of the subsection (H. luteicystidiatum, H. helodes and H. pusillum) by its uniformly brownish orange pileus and by its cheilocystidium apex without abnormal wall thickening.

Description

Description of Hebeloma aurantioumbrinum based on 91 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (7) 10–25 (36) mm diameter; shape often umbonate, occasionally convex, rarely broadly umbonate, strongly umbonate, weakly umbonate or applanate; characters often hygrophanous, occasionally spotting, tomentose or pubescent; margin characters often smooth, occasionally crenulate, rarely involute, scalloped or serrate; viscosity tacky when moist; colour variation often two color, occasionally unicolour; colour at centre occasionally fawn, yellowish brown or ochraceous, rarely cinnamon, greyish brown, umber, dark greyish buff, clay-buff or dark pinkish buff.

  Lamellae: attachment usually emarginate, occasionally adnate, rarely adnexed; maximum depth 2–5 mm; number of complete lamellae 26–39; presence of tears often visible with naked eye, occasionally absent, rarely visible with x10 lens; white fimbriate edge usually present, rarely weak.

  Cortina presence: no.

  Stipe: (10) 15–37 (50) x (1) 2–4 (6) {median} x (1) 2–4 (6) {basal} mm; stipe Q 3.4–11.3; base shape cylindrical, rarely clavate or tapering; floccosity often pruinose, occasionally fibrillose, rarely pruinose at apex, floccose at apex, floccose, weakly floccose or tomentose; rooting usually no, rarely yes; thick rhizoids at base absent;

  Context: Texture firm; stipe interior usually hollow, rarely stuffed; stipe flesh discolouring usually no, rarely yes; slenderness measure 4.4–17.3; smell occasionally raphanoid, odourless or weakly raphanoid, rarely earthy or fruit; taste often mild, rarely weakly raphanoid, weakly bitter or none where recorded.

  Spore deposit colour: often clay-buff or brownish olive.

  Exsiccata characters: Not recorded.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, rarely ovoid; colour in microscope often yellow brown, occasionally brown, brown pale or yellow; guttules usually yes, occasionally no. papilla usually no, occasionally weak; Spore Code: (O1) O2; P0 P1; D1 D2.

  Basidia: 25–41 (43) x (5) 6–10 (11) μm; ave. Q 3.2–4.4; spore arrangement 4 spored;

  Cheilocystidia: main shape usually clavate-stipitate, occasionally gently clavate, capitate-stipitate, clavate-lageniform or clavate-ventricose or clavate, rarely spathulate, spathulate-stipitate, tapering or ventricose; special features observed occasionally apical thickening, septa or median thickening, rarely geniculate, many collapsed in exsiccata, sinuate or yellow contents; cheilocystidia ratios: A/M = 1.57–2.34; A/B = 1.59–2.46; B/M = 0.89–1.18.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 100 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation variable; shape of trama elements beneath subcutis ellipsoid, often oblong.

  Caulocystidia: Similar to cheilocystidia but larger, up to 75 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma aurantioumbrinum's preferred habitat appears to be arctic tundra with soil or boggy, mossy soil. Where only one possible associate was recorded, the most commonly recorded associate was Salix (95.2%) but Cassiope (3.2%) and Alnus (1.6%) were also recorded. In these cases the most commonly recorded family was Salicaceae (94.4%). We have additional records where Betula (5.8%), Picea (1.4%) and Dryas (1.4%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Salicaceae (92.8%), Polygonaceae (14.5%) and Betulaceae (7.2%) 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 Northern America (70.3%), Europe (18.7%) and Temperate Asia (11.0%). 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 (44.0%), unknown biome (34.1%) and temperate conifer forests (16.5%), specifically including the ecoregions: Unknown region (34.1%), Kalaallit Nunaat Arctic steppe (22.0%), South Central Rockies forests (15.4%) and Russian Arctic desert (11.0%). From collector information, it appears collections have been found in the 4.1 Grassland – Tundra (48.9%), 5.10 Wetlands (inland) – Tundra wetlands (inc. pools and temporary waters from snowmelt) (23.3%) and 5.11 Wetlands (inland) – Alpine wetlands (inc. temporary waters from snowmelt) (17.8%) 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 Northern America we have records from Subarctic America (Greenland, Nunavut and Alaska) and Northwestern U.S.A. (Wyoming, Montana and Colorado).

  Within Europe all our records are from the North (Svalbard, Norway, Iceland and Sweden). Specimens have been collected from 59.7°N to 78.9°N.

  Within Temperate Asia we have records from Siberia (Tyumen) and Russian Far East (Chukotka and Sakha).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma aurantioumbrinum is under-represented in the five-locus result; we have not been very successful in obtaining Tef1a sequences from this species. There are more representatives of the species which do form monophyla. Molecularly, H. aurantioumbrinum is sister species to H. helodes, from which it can only be separated based on RPB2 and MCM7. With either of these, H. aurantioumbrinum forms a well-supported species clade. Based on ITS only, H. aurantioumbrinum cannot be distinguished from H. helodes.

• arrow_drop_downarrow_drop_upCommentary
  Given the shape of its cheilocystidia, Hebeloma aurantioumbrinum clearly belongs to H. subsect. Crustuliniformia. The species has not been tested for intercompatibility by Aanen & Kuyper (1999). Within this section, it certainly appears to be confined to boreal, alpine or arctic habitats. In the past it has probably been overlooked or confused with H. minus or H. subconcolor. It can be distinguished from H. minus through the average width of the cheilocystidia apex, which never exceeds 8.5 μm for H. aurantioumbrinum, while the average cheilocystidium apex for H. minus is always greater than 8.5 μm. With regard to H. subconcolor, this species is from H. sect. Velutipes and, as such, has cheilocystidia of the velutipes-type, hence more gently clavate and with a lower average value for the ratio A/M, generally less than 1.6. In determining Hebeloma aurantioumbrinum the combination of characters is important. As a small Hebeloma in an alpine or arctic habitat with the distinctive subsection Crustuliniformia shaped cheilocystidia there are few possibilities and the average spore width (less than 7 μm) and the average cheilocystidium apex (less than 8.5 μm) means it can only be H. aurantioumbrinum. In the few cases when it might be collected in a boreal rather than alpine or arctic habitat, then the small size of the mushroom, the apex of the cheilocystidia that does not show any abnormal wall thickening and the more or less unicoloured brownish orange pileus, separates this species from the other small species of H. subsect. Crustuliniformia, namely: H. luteicystidiatum, H. helodes and H. pusillum.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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