Hebeloma limbatum (Photo: J. Vesterholt)

Taxonomy

Types: ITALY: Tuscany, 2km south of Massa Maritimo along road to Capanne, Grosseto (approx. 44.02°N, 10.15°E, alt. approx. 45 m a.s.l.) in mixed woodland under Quercus cerris, Quercus ilex and Quercus suber, 11 Nov. 2006, J. Vesterholt (06-1153) (Holotype. herbarium acc. no. C C-F-92311 (holotype), BR BR-MYCO 174909-18 (isotype), HJB11858).

• arrow_drop_downarrow_drop_upEtymology
  From limbatus– one colour edged with another, rather broadly to reflect the typically two-coloured appearance of the pileus of (young) specimens of this species. Our collections of this taxon mainly have pileus centre some shade of brown and the margin cream coloured, particularly in younger specimens, although the central brown pigment may disappear in older specimens.

• arrow_drop_downarrow_drop_upDiagnosis
  Hebeloma limbatum possesses the cheilocystidia typical of H. subsect. Clepsydroida. The species shares with H. cavipes the brown pileus colours, the strongly dextrinoid spores and the spore width which is at most 6.5 µm, but differs in the spore Q which is smaller than 1.85 in H. limbatum and at least 1.85 in H. cavipes. In terms of ITS data, H. limbatum is distinct from H. cavipes and all other Hebeloma species, for which the ITS has been sequenced.

Description

Description of Hebeloma limbatum based on 102 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (17) 23–54 (57) mm diameter; shape occasionally convex, umbonate or broadly umbonate, rarely none, umbilicate or strongly umbonate; characters occasionally rugulose, rarely spotting; margin characters often smooth, occasionally scalloped, rarely reflexed, crenulate, involute or ribbed; viscosity tacky when moist; colour variation often unicolour, occasionally two color; colour at centre occasionally cream or yellowish brown, rarely cinnamon, warm buff, pale yellow, pale cream, ochraceous, clay-red, dark pinkish buff or honey.

  Lamellae: attachment usually emarginate, rarely adnate; maximum depth 2–8 mm; number of complete lamellae 48–88; presence of tears often visible with naked eye, occasionally absent or visible with x10 lens; white fimbriate edge often present, rarely weak or very strong.

  Cortina presence: no.

  Stipe: (17) 27–62 (79) x 4–9 (11) {median} x 4–10 (12) {basal} mm; stipe Q 2.5–12.2; base shape often cylindrical, occasionally clavate, rarely bulbous; floccosity occasionally velute, floccose or pruinose, rarely weakly floccose, pruinose at apex, floccose at apex, fibrillose or none; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior often hollow, occasionally stuffed, rarely superior wick; stipe flesh discolouring often no, occasionally yes, rarely weak or very strongly; slenderness measure 3.5–30.0; smell often raphanoid, occasionally weakly raphanoid, rarely cocoa, odourless, fruit or strongly raphanoid; taste often bitter or raphanoid where recorded.

  Spore deposit colour: often brownish olive, occasionally umber or yellowish brown.

  Exsiccata characters: Not recorded.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, usually limoniform; colour in microscope often brown, occasionally yellow brown; guttules often yes, rarely no or weak. papilla often yes, occasionally very strongly, rarely weak; Spore Code: O2 O3; P1 P2; D3 (D4).

  Basidia: (19) 21–36 (37) x 6–9 (10) μm; ave. Q 3.4–4.8; spore arrangement 4 spored;

  Cheilocystidia: main shape clavate-lageniform or clavate-ventricose, often clavate-stipitate, rarely capitate, gently clavate, spathulate-stipitate or ventricose; special features observed often median thickening, occasionally apical thickening, septa or sinuate, rarely rostrate, geniculate or many collapsed in exsiccata; cheilocystidia ratios: A/M = 1.52–2.21; A/B = 0.91–1.68; B/M = 1.34–1.92.

  Pleurocystidia: usually none seen, rarely seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 275 μm; ixocutis hyphae width up to 7 μm; ixocutis hyphae encrustation variable; shape of trama elements beneath subcutis isodiametric or thickly sausage-shaped up to 15 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma limbatum's preferred habitat appears to be deciduous, Mediterranean woodland with calcareous soil and litter. Where only one possible associate was recorded, the most commonly recorded associate was Quercus (93.2%) but Cedrus (1.4%), Picea (1.4%), Cistus (1.4%), Fagus (1.4%) and Helianthemum (1.4%) were also recorded. In these cases the most commonly recorded family was Fagaceae (94.6%). We have additional records where Pinus (5.6%), Arbutus (2.2%), Notholithocarpus (2.2%), Pseudotsuga (2.2%), Arctostaphylos (1.1%) and Populus (1.1%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Fagaceae (94.4%), Pinaceae (10.1%) and Cistaceae (6.7%) The growth habit of our collections was often scattered, occasionally solitary and rarely gregarious or caespitose.

  According to our current data, the species is found on multiple continents with collections found in Europe (70.8%), Northern America (26.0%) and Temperate Asia (3.1%). 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. mediterranean forests, woodlands & scrub (68.3%) and temperate broadleaf & mixed forests (18.8%), specifically including the ecoregions: Northeast Spain and Southern France Mediterranean forests (23.8%), California interior chaparral and woodlands (14.9%) and Southwest Iberian Mediterranean sclerophyllous and mixed forests (10.9%). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (78.0%) and 14.5 Urban Areas (15.3%) 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 we have records from the Southwest (Spain, Portugal and France), the Southeast (Italy, Bulgaria and Malta), the Centre (Netherlands and Germany) and the North (England). Specimens have been collected from 35.9°N to 52.1°N.

  Within Northern America we have records from Southwestern U.S.A. (California), Northwestern U.S.A. (Oregon) and North-central U.S.A. (California).

  Within Temperate Asia all our records are from Caucasus (Adygea).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma limbatum is monophyletic, and reasonably well to highly supported in all single locus analyses and receives full bootstrap support in the results of the concatenated datasets. It does not have any clear affinity to any other species within the section. BLAST results against UNITE, retrieving three ITS sequences from unidentified material (GQ478005, EF411103, HM849636), suggest that H. limbatum, or a very close relative, also occurs in the USA and associates with American oaks.

• arrow_drop_downarrow_drop_upCommentary
  Given the shape of its cheilocystidia and its spores at most O3, P2, H. limbatum clearly belongs to H. sect. Denudata subsect. Clepsydroida. This species most likely corresponds to ICG20 of Aanen & Kuyper (1999). The pileus colour, with distinct brown tones in the centre (which may disappear with age) and the paler margin, together with its spores, strongly dextrinoid and with average width at most 6.5 μm and average Q less than 1.85, distinguish this species. It is similar to H. cavipes, but it can be separated from that species based on the lower Q value for the spores.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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