Hebeloma viscidissimum (Photo: N. Siegel)

Taxonomy

Basionym:
Gymnopilus viscidissimus Murrill, Mycologia 4 (5): 256 (1912)

Types: UNITED STATES: Oregon: Mill City (approx. 44.759°N, 122.4797°W, alt. approx. 300 m a.s.l.) on mossy soil and litter in shrubland, 9 Nov. 1911, W.A. Murrill (WAM833) (Holotype. herbarium acc. no. NY 775296, HJB1000587).

Heterotypic synonyms:

• Hebeloma amarellum A.H. Sm., V.S. Evenson & Mitchel, The Veiled Species of Hebeloma in the Western United States: 100 (1983)
• Hebeloma pinetorum A.H. Sm., V.S. Evenson & Mitchel, The Veiled Species of Hebeloma in the Western United States: 102 (1983)

Homotypic synonyms:

• Flammula viscidissima (Murrill) Murrill, Mycologia 4 (5): 262 (1912)

• arrow_drop_downarrow_drop_upEtymology
  From viscidus (Latin, adj) meaning viscid to emphasize the “very slimy” pileus.

• arrow_drop_downarrow_drop_upDiagnosis
  Pileus conic, not fully expanding, gregarious, 2 cm. broad; surface smooth, glabrous, very slimy, isabelline with an incarnate tint, usually a little darker at the center; lamellae sinuate-adnate, broad, ventricose, rather crowded, pale-isabelline, becoming darker with age; spores ovoid, pointed, often one-sided, very pale with a fuscous tint under a microscope, dark-fulvous in mass, 7 × 3–4 µ; stipe equal or slightly larger below, stuffed, whitish, furfuraceous above, fibrillose below, rather tough, 6 cm. long, 3.5 mm. thick.

Description

Description of Hebeloma viscidissimum based on 18 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (10) 16–43 (75) mm diameter; shape usually convex, occasionally umbonate or broadly umbonate, rarely applanate or weakly umbonate; characters often remains of universal veil, occasionally spotting; margin characters usually involute, occasionally crenulate or fibrillose; viscosity tacky when moist; colour variation usually unicolour, occasionally two color; colour at centre often dark pinkish buff, occasionally cinnamon or yellowish brown.

  Lamellae: attachment often emarginate, occasionally adnate, rarely adnexed or decurrent tooth; maximum depth up to 4 mm; number of complete lamellae 41–56; presence of tears absent; white fimbriate edge weak.

  Cortina presence: no.

  Stipe: (20) 26–89 (105) x 2–6 (9) {median} x 2–7 (11) {basal} mm; stipe Q 4.3–33.3; base shape usually cylindrical, often clavate, rarely tapering; floccosity usually fibrillose, often pruinose at apex, occasionally floccose, rarely pruinose; rooting often no, occasionally yes or weak; thick rhizoids at base absent;

  Context: Texture firm; stipe interior hollow, occasionally superior wick; stipe flesh discolouring usually yes, rarely no; slenderness measure 6.4–92.9; smell usually odourless, rarely cocoa; taste usually bitter, occasionally mild where recorded.

  Spore deposit colour: Not recorded.

  Exsiccata characters: dark, pileus blackening or stipe blackening.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid; colour in microscope occasionally brown, yellow or yellow brown; guttules often no, occasionally yes. papilla usually no, rarely weak; Spore Code: (O1) O2; (P0) P1; D3.

  Basidia: 19–33 (35) x 4–7 μm; ave. Q 3.8–4.4; spore arrangement 4 spored;

  Cheilocystidia: main shape usually cylindrical, occasionally gently clavate or filiform, rarely clavate; special features observed often branching, septa or conglutinate, occasionally clamped septa, many collapsed in exsiccata or bifurcate; cheilocystidia ratios: A/M = 1.07–1.22; A/B = 1.05–1.23; B/M = 0.90–1.11.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 190 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation no; shape of trama elements beneath subcutis cylindrical, occasionally isodiametric or ovate up to 18 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 viscidissimum's preferred habitat appears to be coniferous woodland with mossy soil and litter or mossy soil. Where only one possible associate was recorded, the most commonly recorded associate was Picea (80.0%) but Pseudotsuga (20.0%) were also recorded. In these cases the most commonly recorded family was Pinaceae (100.0%). We have additional records where Tsuga (36.4%), Abies (18.2%), Gaultheria (9.1%) and Pinus (9.1%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Pinaceae (90.9%) and Ericaceae (9.1%) The growth habit of our collections was often scattered and occasionally gregarious or caespitose.

  According to our current collections, the species is found only in Northern America. On the continent, collections have been found only in the temperate conifer forests WWF biome 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. (Central-Southern Cascades Forests (33.3%), Northern California coastal forests (22.2%), Central Pacific Northwest coastal forests (16.7%), Puget lowland forests (11.1%) and North Cascades conifer forests (11.1%) ecoregions). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (62.5%), 1.1 Forest – Boreal (12.5%), 14.2 Pastureland (12.5%) and 3.4 Shrubland –Temperate (12.5%) 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 Northern America we have records from Northwestern U.S.A. (Washington, Oregon and Idaho), Southwestern U.S.A. (California) and Western Canada (British Columbia).

• arrow_drop_downarrow_drop_upCommentary
  With the mainly cylindrical cheilocystidia, on average less than 40 µm and the spores small, weakly ornamented and rather strongly dextrinoid this belongs to Hebeloma sect. Scabrispora. Within this section, the spores, with average length between 7.5–9.0 µm and average Q less than 1.65, not distinctly ornamented nor with a consistently loosening perispore and an indistinct papilla, together with the number of full-length lamellae less than 70 indicates a unique species. Until the discovery of this Murrill collection we were referring to this species as H. amarellum, but the name Hebeloma viscidissimum takes priority. Hence, H. amarellum, and also H. pinetorum which is conspecific, should be synonymized with H. viscidissimum. Unfortunately we were unable to generate any DNA sequence data from the material. Kauffman (1926) interpreted this species as a Cortinarius but Hesler (1969), in his monograph on Gymnopilus of North America, stated that “The dark-tawny spores, the inconspicuous, clavate cheilocystidia, the lack of a veil, the gelatinous cuticle, and the habitat all suggest Hebeloma”. Hesler, in 1974, left a herbarium note confirming his view that this was a Hebeloma. Halling (1986) pointed out that this was a Hebeloma, referencing Hesler (1969).

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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