Hebeloma plesiocistum (Photo: X. Llimona)

Taxonomy

Types: SPAIN: Barcelona, Can Ferrer (Barcelona) (approx. 41.67°N, 2.21°E, alt. approx. 285 m a.s.l.) on acidic soil in maquis under Cistus monspeliensis, 14 Dec. 2002, X. Llimona, J. Vila, T. Jimenez (Holotype. herbarium acc. no. LIP JVG1021214-5, HJB11514).

• arrow_drop_downarrow_drop_upEtymology
  An adjective, from the Greek plesios– neighbouring, and Kistus– Cistus.

• arrow_drop_downarrow_drop_upOriginal diagnosis
  Pileus usque ad 50 mm in diam., convexus vel applanatus, aut leviter depressus; superficies sicca vel leviter viscida, haud hygrophana, haud striata, pallide brunnea vel bruno ochracea, a denso strato pruinae griseae vel pallide griseae, irregulariter distributae, obtecta. Lamellae adnatae vel subdecurrentes, parce densae, tenues; color saturate cremeus, alutaceus vel brunneoalutaceus pallidus, demum brunneo-tabacinus. Acies fimbriata. Stipes centralis vel leviter excentricus, teres, usque ad 70–15 mm; candidus vel pallide alutaceus; superficies sicca, nonnullas squamas obtecta. Cortina non visa. Caro cremea vel pallide brunnea; odor compositus (cacao et raphanoideus). Sporae amygdaloideae, fere laeves vel inconspicue ornamentatae, maxime dextrinoideae; 9.9–12.5 x 5.8–6.6 μm. Basidia tetrasporica, 25–41 x 6.7–9.5 μm, cylindrica vel clavata. Pleurocystidia non visa. Cheilocystidia 38–52 x 7.3–8.9 x 4.4–4.9 x 5.9–6.9 μm, clavata vel subcapitata. Caulocystidia cheilocystidiiformia. Pileipellis, ixocutis a parce tenui epicute, usque ad 80 μm crasso, obtecta. Hyphae inclusae, 2–6 μm in diam., laeves vel raro incrustatae, hyalinae vel aliquando pigmentatae. Fibulae omnipraesentes.

• arrow_drop_downarrow_drop_upEnglish translation
  Pileus up to 50 mm in diam., convex or plano-convex, then applanate with a shallow central depression; surface dry or slightly viscid, neither hygrophanous nor striate, pale brown or ochraceous brown with a dense pruinose layer; pruina grey or pale grey, often patchy. Lamellae adnate to subdecurrent, moderately dense, thin, cream, alutaceous or brown when young, later tabac-brown, edge fimbriate. Stipe central or somewhat excentric, straight, up to 70 × 15 mm; white or alutaceous; surface dry, with scattered squamules. Cortina not observed. Flesh cream or pale brown. Smell cacao, mixed with a raphanoid component. Spores amygdaloid, almost smooth to very weakly ornamented, very strongly dextrinoid, 9.9–12.5 × 5.8–6.6 μm. Basidia four-spored, 25–41 × 6.7–9.5 μm. Pleurocystidia not found. Cheilocystidia 38–52 × 7.3–8.9 × 4.4–4.9 × 5.9–6.9 μm, clavate to subcapitate. Caulocystidia resemble cheilocystidia. Pileipellis ixocutis with a relatively thin epicutis up to 80 μm, embedded hyphae 2–6 μm broad, smooth or rarely encrusted, hyaline or occasionally pigmented. Clamp connections present throughout the basidiome.

Description

Description of Hebeloma plesiocistum based on 7 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (21) 25–39 (50) mm diameter; shape often convex, occasionally umbilicate or strongly umbonate; characters occasionally pruinose; margin characters smooth, often eroded, involute, reflexed, ribbed or wavy; viscosity tacky when moist; colour variation often unicolour, occasionally two color; colour at centre occasionally ochraceous, cinnamon or clay-buff.

  Lamellae: attachment often emarginate, occasionally adnate or decurrent tooth; maximum depth up to 4 mm; number of complete lamellae 52–60; presence of tears absent; white fimbriate edge often present or weak.

  Cortina presence: no.

  Stipe: (15) 16–51 (68) x 6–10 (14) {median} x 5–10 (15) {basal} mm; stipe Q 2.1–5.3; base shape often cylindrical or tapering, occasionally clavate; floccosity often pruinose, occasionally floccose, weakly floccose or pruinose at apex; rooting no; thick rhizoids at base absent;

  Context: Texture firm; stipe interior hollow or stuffed; stipe flesh discolouring no; slenderness measure 1.1–6.5; smell often strongly raphanoid, occasionally cocoa, raphanoid or weakly raphanoid; taste raphanoid where recorded.

  Spore deposit colour: Not recorded.

  Exsiccata characters: Not recorded.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid; colour in microscope often yellow brown, occasionally yellow or yellow pale; guttules yes. papilla often no, occasionally weak; Spore Code: O1 O2; P0 (P1); D3 D4.

  Basidia: 21–39 (40) x 6–9 μm; ave. Q 3.5–4.2; spore arrangement 4 spored;

  Cheilocystidia: main shape clavate-lageniform or clavate-ventricose, usually ventricose, occasionally lageniform or subcapitate; special features observed often septa, occasionally basal thickening, bifurcate, branching or short; cheilocystidia ratios: A/M = 1.52–1.85; A/B = 1.00–1.28; B/M = 1.37–1.57.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 80 μm; ixocutis hyphae width up to 5 μm; ixocutis hyphae encrustation often no, occasionally yes; shape of trama elements beneath subcutis often cylindrical, occasionally ovate.

  Caulocystidia: Similar to cheilocystidia but larger, up to 90 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma plesiocistum's preferred habitat appears to be maquis with acidic soil. Where only one possible associate was recorded, that associate has always been Cistus (family Cistaceae). We have additional records where Quercus was recorded as a possible associate, but for these collections a number of possible associates were mentioned. Overall the most commonly recorded families are Cistaceae (100.0%) and Fagaceae (16.7%) The growth habit of our collections was often scattered and occasionally solitary.

  According to our current collections, the species is found only in Europe. On the continent, collections have been found only in the mediterranean forests, woodlands & scrub 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. (Northeast Spain and Southern France Mediterranean forests (50.0%), Tyrrhenian-Adriatic sclerophyllous and mixed forests (33.3%) and Italian sclerophyllous and semi-deciduous forests (16.7%) ecoregions). From collector information, it appears collections have been found only in the 3.8 Shrubland – Mediterranean-type shrubby vegetation IUCN habitat 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 (Italy, Spain and France) and the Southeast (Italy). Specimens have been collected from 39.6°N to 42.5°N.

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma plesiocistum forms a well-bootstrap-supported monophylum in phylogenetic analyses, is molecularly distinct and can be identified by any of the loci tested (Eberhardt et al. 2013). The closest phylogenetic relatives of this taxon appear to be H. parvicystidiatum and H. alboerumpens, of which only the latter is Cistus-associated.

• arrow_drop_downarrow_drop_upCommentary
  The combination of almost smooth to very weakly ornamented and strongly dextrinoid spores, the short hourglass (clavate-lageniform) cheilocystidia and the pruinose pileus indicate H. sect. Theobromina, as do the molecular results of a multi-locus dataset (Eberhardt et al. 2013). Hebeloma plesiocistum can be distinguished from other species of this section by means of its wide spores (>5.5 μm) and its cheilocystidia with a large average apex (> 7 μm). It is interesting to note that the holotype has unusually long cheilocystidia for this section of Hebeloma. It is the only collection we have from the whole section where the average cheilocystidium length is greater than 40 μm. We await further collections of this taxon to test our view of the species delimitation.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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