Hebeloma pusillum (Photo: P.B. Hansen)

Taxonomy

• arrow_drop_downarrow_drop_upNomenclatural notes
  Replacemant name for Hebeloma pusillum J.E. Lange (1938).

Types: Lange, Danmarks Agaricaceer. Held at Herbarium, Natural History Museum of Denmark, University of Copenhagen: 4 (1893-1910) pl. 460, lectotype (icon) designated by Beker et al., Hebeloma (Fr.) P. Kumm.: (2016) page 257 (MBT202550) DENMARK: F, Langesoskovene s of Morud UTM NG7444 TBU 29 (55.434°N, 10.199°E, alt. approx. 30 m a.s.l.) on boggy soil in willow thicket under Salix sp., 16 Oct. 1991, J. Vesterholt (91-685) (Epitype. herbarium acc. no. C JV-91-685, HJB1000128). Epitype designated by Vesterholt, Fungi N. Eur. 3. 3: (2005) page 82.

• arrow_drop_downarrow_drop_upType notes
  The lectotype was C Danmarks Agaricaceer pl. 460, later reproduced as plate 120c in Lange, Fl. Agric. Danica 3 (1938).

Heterotypic synonyms:

• Hebeloma pusillum var. longisporum Bruchet, Bull. Mens. Soc. Linn. Lyon 39, supplement 6: 126 (1970)
• Hebeloma vaccinum var. cephalotum Enderle & Vesterh., Die Pilzflora des Ulmer Raumes: 379 (2004)

Homotypic synonyms:

• Hebeloma pusillum J.E. Lange, Dansk Botanisk Arkiv 9 (6): 6 (1938)
• Hebelomatis pusillum (J.E. Lange) Locq. ;, Flore Mycologique Vol III - Text. Cortinariales A: 146 (1979) ["1977"]

• arrow_drop_downarrow_drop_upEtymology
  From pusillus- very small, emphasizing the stature of this taxon.

• arrow_drop_downarrow_drop_upOriginal diagnosis
  Pileo 0.8–2 cm, e conico-convexo expanso, alutaceo; ubone minuto, prominente, spadiceo-rufo; velo nullo. Lamellis latis, margine guttulatis, e pallido incarnato-argillaceis. Stipite 2–4 cm x 1–2.5 mm, albo, pulverulento. Odor leviter raphanoideus. Sporis ellipsoideo-limoniformibus, 12–13 x 6 μm. Cystidiis clavatis, 45–60 x 6–11 μm. In Salicetis paludosis. 1907.

• arrow_drop_downarrow_drop_upEnglish translation
  Pileus 0.8–2 cm, conico-convex, expanding with age, yellowish with small, prominent, reddish brown umbo; veil absent. Lamellae broad, with weeping edge, first pale then flesh-coloured pale brown. Stipe 2–4 cm × 1–2.5 mm, white, pulverulent. Smell slightly raphanoid. Spores ellipsoid to limoniform, 12–13 × 6 μm. Cystidia clavate, 45–60 × 6–11 μm. In marshy Salix copses, 1907.

Description

Description of Hebeloma pusillum based on 38 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (5) 11–27 (40) mm diameter; shape usually convex, occasionally umbonate, rarely umbilicate or strongly umbonate; characters Not recorded; margin characters usually smooth, occasionally involute, reflexed or scalloped; viscosity tacky when moist; colour variation usually two color, rarely unicolour; colour at centre occasionally dark brick or umber, rarely cinnamon, brick or sepia.

  Lamellae: attachment emarginate, rarely adnate or decurrent tooth; maximum depth 3–4 mm; number of complete lamellae 20–48; presence of tears often visible with naked eye, occasionally absent or visible with x10 lens; white fimbriate edge usually present, rarely weak.

  Cortina presence: no.

  Stipe: (14) 18–40 (58) x 1–3 (6) {median} x (1) 2–4 (6) {basal} mm; stipe Q 6.7–23.2; base shape cylindrical, rarely clavate; floccosity often pruinose, occasionally weakly floccose or pruinose at apex, rarely fibrous; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior often hollow or stuffed; stipe flesh discolouring usually yes, rarely no; slenderness measure 8.5–64.1; smell often raphanoid, occasionally odourless, rarely weakly raphanoid or cocoa; taste raphanoid where recorded.

  Spore deposit colour: often brownish olive, occasionally umber.

  Exsiccata characters: often fragile, occasionally dark.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, often fusoid, rarely limoniform; colour in microscope often brown, occasionally yellow brown; guttules variable. papilla often no, occasionally weak, rarely very strongly; Spore Code: O2 O3; (P0) P1 P2; (D0) D1 (D2).

  Basidia: (23) 24–38 (39) x (5) 6–10 μm; ave. Q 3.0–4.4; spore arrangement Not recorded;

  Cheilocystidia: main shape usually capitate-stipitate or clavate-stipitate, occasionally clavate or clavate-lageniform or clavate-ventricose, rarely gently clavate, spathulate-stipitate or ventricose; special features observed occasionally many collapsed in exsiccata, rarely median thickening, septa, conglutinate, short or uniform; cheilocystidia ratios: A/M = 1.66–2.71; A/B = 1.10–2.52; B/M = 0.94–1.63.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 80 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation yes; shape of trama elements beneath subcutis often ellipsoid or thickly sausage-shaped, occasionally angular, cylindrical or oblong up to 18 μm wide.

  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 pusillum's preferred habitat appears to be willow thicket with boggy soil. Where only one possible associate was recorded, the most commonly recorded associate was Salix (95.7%) but Alnus (4.3%) were also recorded. In these cases the most commonly recorded family was Salicaceae (95.7%). We have additional records where Betula (15.2%), Populus (6.1%), Picea (6.1%) and Pinus (3.0%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Salicaceae (97.0%), Betulaceae (30.3%) and Pinaceae (9.1%) The growth habit of our collections was occasionally scattered, gregarious, caespitose or solitary.

  According to our current collections, the species is found only in Europe. On the continent, collections have been found only in the temperate broadleaf & mixed 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. (European Atlantic mixed forests (27.3%), Western European broadleaf forests (24.2%) and Baltic mixed forests (15.2%) ecoregions). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (40.0%), 5.4 Wetlands (inland) – Bogs, marshes, swamps, fens, peatlands (26.7%), 5.3 Wetlands (inland) – Shrub dominated wetlands (20.0%) and 17.1 Quarry (13.3%) 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 North (Denmark, Isle Of Man, Norway and Wales), the Centre (Germany, Belgium and Netherlands) and the Southwest (France, Spain and Italy). Specimens have been collected from 42.3°N to 60.1°N.

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma pusillum forms species clades in all of the loci tested, and receives bootstrap support in all single locus results apart from ITS and Tef1a. For the latter, sequence data could to date only be obtained from a single collection.

• arrow_drop_downarrow_drop_upCommentary
  Given the shape of its cheilocystidia, Hebeloma pusillum clearly belongs to H. subsect. Crustuliniformia. The species most likely corresponds to ICG8 of Aanen & Kuyper (1999). It can be readily distinguished from the other members of this subsection, which grow in lowland areas, based on the distinctly two-coloured pileus, the number of lamellae, between 20 and 40, the slender basidiomes with stipe width at most 3.5 mm and stipe Q normally larger than 12, the spore length, greater than 11 μm, the large average width of the cheilocystidium apex, at least 8 μm, and with no regular apical thickening of the cheilocystidium wall. It has probably often been confused with H. helodes, which is also a small Hebeloma sp., but H. pusillum is confined to Salix, has a more fragile stature and usually a rather darker centre to the pileus and significantly longer spores, on average. Hebeloma luteicystidiatum also has long spores, but the very distinct apical thickening of the cheilocystidium wall distinguishes this taxon from H. pusillum, which rarely has any apical thickening of the cheilocystidium. Hebeloma aurantioumbrinum is rare in non-arctic/alpine environments, but also has shorter spores, on average. Hebeloma minus is also rare in non arctic/alpine environments, but, in any case, this taxon has a smaller spore Q from that of H. pusillum. Hebeloma salicicola could be confused with H. pusillum, but normally it has a more robust stature with a wider stipe, a smaller stipe Q and the spores of H. salicicola are, on average, more dextrinoid. Having studied the description and holotype material of Hebeloma vaccinum var. cephalotum, we are convinced this was a mixed collection of H. salicicola and H. pusillum. We have extracted DNA several times and every sequence we have generated is of H. pusillum, similarly, the material we have examined is H. pusillum. However, the macroscopic description in the protologue for this taxon very much more resembles H. salicicola. We have also examined the isotype of this material, but that is H. vaccinum. So we conclude that we should synonymize H. vaccinum var. cephalotum with H. pusillum but point out that the macroscopic description does not really match H. pusillum. We have examined the description and holotype material of H. pusillum var. longisporum, both morphologically and molecularly, and have concluded that there are no grounds for separating this variety, as did Gröger (1987a). The molecular sequences we have generated are identical to H. pusillum and our measurements of the spore length show it to be in the middle of the range for this species. The original iconotype of Lange is an excellent representation of this taxon. The epitype selected by Vesterholt is also representative. It is possible that H. magnimamma represents this taxon, however, we cannot be sure and hence we prefer not to formalize this synonymy.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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