Hebeloma populinum (Photo: M. Maletti)

Taxonomy

Types: FRANCE: Oise, Bet Cramoisy and Saint-Vaast-les-Mello (Oise) (approx. 49.25°N, 2.4°E, alt. approx. 80 m a.s.l.) on boggy soil and litter in deciduous woodland under Populus nigra and Populus sp., 13 Aug. 1959, H. Romagnesi (R59-99) (Holotype. herbarium acc. no. PC 0090762, HJB1000030).

• arrow_drop_downarrow_drop_upEtymology
  From the habitat with Populus.

• arrow_drop_downarrow_drop_upOriginal diagnosis
  Pileo (1,5) 2–6 cm, simili pileo H. crustuliniforme cum figura tum colore pallido, viscidulo, interdum subtilissime virgatulo. Stipite 2–6 cm x 3–8 mm, subcylindrato, aut inferne attenuato ac torto, superne candido, paulum fuscescente, praesertim in parte inferiore, eximie sursum farinoso. Carne in stipite paulum fuscescente; odore gravi, potius cacaino quam rapaceo, sapore amaro. Lamellis stipatis, alte sinuato-liberis, segmentiformibus vel subventricosis. argillaceis, acie albida ac plorante. Sporis in cumulo umbrinis, amygdaliformibus, (11)–12–13,7 x 6,7–8–(8,5) μm, verruculosis, intensius s.m. coloratis. Pilis acierum claviformibus, 54–90 x 7,5–13,5 μm. Epicute ex hyphis filiformibus, sed sursum clavatis praedito, cute hyphis cylindratis, membrana pallide colorata. - Sub Populis nigris ac affinibus, in locis paludosis.

• arrow_drop_downarrow_drop_upEnglish translation
  Pileus (1.5) 2–6 cm, looking similar to that of H. crustuliniforme not only in appearance but also the pale colour, slightly viscid, sometimes subtly virgate. Stipe 2–6 cm × 3–8 mm, subcylindrical or attenuated-twisted towards base, white above, weakly browning, especially in lower part, at apex remarkably pruinose. Context in stipe weakly browning; smell strong, rather more like cocoa than raphanoid; taste bitter. Lamellae crowded, narrowly sinuate to free, segmentiform to subventricose, clay-coloured, with white edge exuding droplets. Spores in mass umber brown, amygdaloid, (11)–12–13.7 × 6.7–8–(8.5) μm, warted, intensely coloured under microscope. Marginal hairs claviform, 54–90 × 7.5–13.5 μm. Epicutis made of filiform hyphae, but with clavate apex; cutis of cylindrical hyphae with pale coloured membranes. Under Populus nigra and similar hybrids in moist places.

Description

Description of Hebeloma populinum based on 11 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (15) 20–37 (60) mm diameter; shape often convex, occasionally broadly umbonate; characters occasionally spotting; margin characters often involute, occasionally crenulate or smooth; viscosity tacky when moist; colour variation often unicolour, occasionally two color; colour at centre occasionally cream, pinkish buff or ochraceous.

  Lamellae: attachment often emarginate, occasionally adnate; maximum depth 6–7 mm; number of complete lamellae 35–80; presence of tears visible with naked eye; white fimbriate edge present.

  Cortina presence: no.

  Stipe: (20) 35–48 (70) x (3) 5–6 (8) {median} x (3) 5–10 (15) {basal} mm; stipe Q 4.3–14.0; base shape cylindrical, often clavate; floccosity often floccose or pruinose, occasionally pruinose at apex; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior hollow, often stuffed, occasionally superior wick; stipe flesh discolouring often no, occasionally yes or weak; slenderness measure 6.2–23.9; smell occasionally cocoa, raphanoid, odourless or weakly raphanoid; taste often bitter, occasionally weakly bitter or raphanoid where recorded.

  Spore deposit colour: umber.

  Exsiccata characters: Not recorded.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid or limoniform; colour in microscope brown; guttules often no, occasionally weak. papilla often very strongly, occasionally yes; Spore Code: O3 O4; P2 P3; D3 D4.

  Basidia: (28) 29–46 (47) x 6–11 μm; ave. Q 3.8–5.0; spore arrangement 4 spored;

  Cheilocystidia: main shape usually clavate-stipitate, often capitate-stipitate, occasionally spathulate-stipitate or clavate-lageniform or clavate-ventricose, rarely capitate; special features observed often apical thickening or median thickening, occasionally septa or conglutinate, rarely branching, irregular, many collapsed in exsiccata or sinuate; cheilocystidia ratios: A/M = 1.47–2.72; A/B = 1.49–3.23; B/M = 0.73–1.53.

  Pleurocystidia: usually none seen, rarely only close to lamella edge.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 135 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation yes; shape of trama elements beneath subcutis often ellipsoid, ovate, thickly sausage-shaped, thinly sausage-shaped or spherical 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 populinum's preferred habitat appears to be slagheap or deciduous woodland with soil, boggy soil and litter or grassy soil. Where only one possible associate was recorded, the most commonly recorded associate was Populus (50.0%) but Salix (50.0%) were also recorded. In these cases the most commonly recorded family was Salicaceae (100.0%). We have additional records where Tilia (14.3%) and Quercus (14.3%) 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%), Malvaceae (14.3%) and Fagaceae (14.3%) The growth habit of our collections was usually gregarious and occasionally scattered.

  According to our current collections, the species is found only in Europe. On the continent, 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. temperate broadleaf & mixed forests (71.4%) and mediterranean forests, woodlands & scrub (28.6%), specifically including the ecoregions: Po Basin mixed forests (42.9%), English Lowlands beech forests (14.3%), Pindus Mountains mixed forests (14.3%), Italian sclerophyllous and semi-deciduous forests (14.3%) and European Atlantic mixed forests (14.3%). From collector information, it appears collections have been found in the 17.1 Quarry (33.3%), 1.4 Forest – Temperate (33.3%), 14.5 Urban Areas (22.2%) and 5.3 Wetlands (inland) – Shrub dominated wetlands (11.1%) 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 Southeast (Italy and Greece), the Centre (Poland), the Southwest (Italy and France) and the North (England). Specimens have been collected from 40.1°N to 51.5°N.

• arrow_drop_downarrow_drop_upMolecular results
  See also under H. echinosporum. Hebeloma populinum is molecularly clearly distinct (monophyletic, with bootstrap support) from all other Hebeloma species apart from H. echinosporum. It appears that these two species may form mixed clades based on the two mitochondrial loci.

• arrow_drop_downarrow_drop_upCommentary
  The spores with strongly warty, almost spiny, ornamentation, constantly loosening perispore and very strongly dextrinoid, together with the shape of the cheilocystidia, firmly put this taxon in H. subsect. Echinospora. It is distinguished from other members of this subsection by the average size of the apex of the cheilocystidium (greater than 7.5 μm) and the spore length (in excess of 12.5 μm). We need further collections of this species before we can comment further on species delimitation. Hebeloma populinum has in the past been confused with H. ammophilum (see for example Vesterholt 2005), which is also associated with Salicaceae and has similarly large spores. However, the spores of H. populinum are somewhat more ornamented with a distinct spiny look when viewed at high magnification. For mature spores, the constantly loosening perispore is also a feature of this taxon. There are many records of Hebeloma populinum, probably on account of the epithet which has led to many Hebeloma collections under Populus being referred to this taxon. On our database we have 33 collections that had been originally determined as H. populinum; they turned out to be H. aanenii, H. aestivale, H. birrus, H. cavipes, H. celatum, H. crustuliniforme, H. eburneum, H. erebium, H. geminatum, H. hiemale, H. leucosarx, H. lutense, H. matritense, H. quercetorum, H. rostratum, H. salicicola, H. vaccinum and H. velutipes. Hebeloma populinum, although widespread, is certainly rare.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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