Hebeloma eburneum (Photo: J. Vesterholt)

Taxonomy

Types: MOROCCO: Azrou (33.4167°N, 5.2167°W, alt. approx. 1500 m a.s.l.) under Cedrus libanotica ssp.atlantica, 8 Nov. 1941, G. Malençon (1122) (Holotype. herbarium acc. no. MPU GM-1122, HJB1000095).

Heterotypic synonyms:

• Hebeloma albocolossum M.M. Moser, Sydowia 38: 174 (1986) ["1985"]
• Hebeloma crustuliniforme var. tiliae Bresinsky, Z. Mykol. 53 (2): 294 (1987)
• Hebeloma ochroalbidum Bohus, Annales Historico-Naturales Musei Nationalis Hungarici 64: 71 (1972)
• Hebeloma perpallidum M.M. Moser, Zeitschrift fuer Pilzkunde 36 (1-2): 72 (1970)
• Hebeloma coniferarum A.H. Sm., V.S. Evenson & Mitchel, The Veiled Species of Hebeloma in the Western United States: 111 (1983)
• Hebelomatis perpallidum (M.M. Moser) Locq. 1979, Flore Mycologique Vol III - Text. Cortinariales A: 146 (1979) ["1977"]

Homotypic synonyms:

• Hebelomatis eburneum (Malençon) Locq. 1979, Flore Mycologique Vol III - Text. Cortinariales A: 146 (1979) ["1977"]

• arrow_drop_downarrow_drop_upEtymology
  From eburneus– ivory white, i.e. white with a yellow tinge, the colour of the pileus.

• arrow_drop_downarrow_drop_upOriginal diagnosis
  Pileo 6–10 cm lato, firmo, spisso, e fornicato applanato vel depresso, magis minusve lobato, cute versus marginem separabili, laevi, viscosa, eburnea, in medio pallide ochraceo late colorata, interdum subtilites virgate; margine primum involute, ex albo concolore, aequali vel breviter costulata. Stipe confluent, 60–80 x 10–20 mm, robusto, firmo, e replete cavo, fibroso, cylindraceo, albido, in senectute deorsum lucide sordido, absque cortina sed usque ad basim toto floccoso vel flocculoso. Lamellis 5–8 mm lat., confertis, inaequalibus, uncinatis vel liberis, pallide argillaceis, roseo-ochraceis dein leviter rufulis, acie granulosa albida interdum lacrymante guttulataque. Carne ex albido pallide lutea, in stipites deorsum leviter sordida, dulci, debili fugacei raphaniodora. Acie lamellarum pilis magnis claviformibus deorsum fibulatis sterili, 50–65 x 8–10 μm. Pleurocystidiis nullis. Basidiis claviformibus 4-sporis, 30–42 x 8–11,5 μm, steigmatis 4–5 μm alt. exclusis. Sporis amygdaliformibus sursum subpapillatus, e brunneo-flavis fulvo luteis s.l., omnino subtiliter granulosis usque ad apiculum, magnitudine variabili: 9.5–12,5 x 5,5–6,5 (7) μm, saepius 11.5–12 x 6–6,5 μm, vel. 12–14,4 x 6,2–7,4 μm, saepius: 12,8–13 x 6,8–7,2 μm. Hab. – Solitarium vel fasciculatum, orbes vel partim orbes faciens, sub tegmine cedrorum (Cedrus libanotica ssp. atlantica) in medio Atlante mense novembri.

• arrow_drop_downarrow_drop_upEnglish translation
  Pileus 6–10 cm broad, firm, compact, convex then expanded to depressed, more or less strongly lobate, cuticle separable near margin, smooth, viscid, ivory, at centre pale ochraceous, sometimes delicately virgate; with margin involute at first, white then with same colour as rest of pileus, equal or slightly ribbed. Stipe confluent (with pileus), 60–80 × 10–20 mm, robust, firm, solid then hollow, fibrous, cylindrical, white, becoming sordid shiny with age, without cortina but down to the base entirely floccose to flocculose. Lamellae 5–8 mm broad, crowded, unequal, uncinate to free, pale brown, pinkish ochre then somewhat reddish, with white, granulose edge, which sometimes sheds droplets. Context first white then pale yellow, in base of stipe sordid, sweet, with weak raphanoid odour. Lamella edge with large, sterile marginal hairs, claviform with clamped base, 50–65 × 8–10 μm. Pleurocystidia absent. Basidia claviform, four-spored, 30–42 × 8–11.5 μm, excluding the 4–5 μm long sterigmata. Spores amygdaloid, subpapillate at apex, brown yellow then reddish yellow, entirely delicately granulose up to apiculus; with large variability in size: 9.5–12.5 × 5.5–6.5 (7) μm, often 11.5–12 × 6–6.5 μm, or 12–14.4 × 6.2–7.4 μm, or 12.8–13 × 6.8–7.2 μm. Habitat: solitary or in clusters, in circles or half circles under the canopy of Cedrus libani subsp. atlantica in the middle Atlas region in the month of November.

Description

Description of Hebeloma eburneum based on 230 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (8) 22–77 (133) mm diameter; shape often convex, occasionally broadly umbonate, rarely umbonate, applanate, strongly umbonate or weakly umbonate; characters rarely spotting, hygrophanous, pruinose, remains of universal veil or rimulose; margin characters often smooth, occasionally involute, rarely scalloped, crenulate, eroded, fibrillose, serrate or wavy; viscosity tacky when moist; colour variation often unicolour, occasionally two color; colour at centre occasionally cream, pale yellow or pale cream, rarely yellowish brown, dark pinkish buff, warm buff, pinkish buff, ochraceous, brownish olive, buff-yellow, pale pinkish buff, clay-buff, umber or sepia.

  Lamellae: attachment usually emarginate, rarely adnate or adnexed; maximum depth 2–9 mm; number of complete lamellae 34–120; presence of tears usually visible with naked eye, rarely absent or visible with x10 lens; white fimbriate edge usually present, rarely weak, very strong or absent.

  Cortina presence: no.

  Stipe: (10) 25–75 (106) x (2) 4–15 (36) {median} x (2) 5–17 (33) {basal} mm; stipe Q 1.6–17.3; base shape often cylindrical, occasionally clavate, rarely bulbous, tapering or subbulbous; floccosity often floccose, occasionally pruinose at apex or pruinose, rarely floccose at apex, fibrillose, weakly floccose or velute; rooting no; thick rhizoids at base usually absent, rarely present;

  Context: Texture firm; stipe interior often stuffed or hollow, rarely superior wick; stipe flesh discolouring often no, rarely yes, weak or very strongly; slenderness measure 1.0–20.0; smell often raphanoid, occasionally odourless, rarely cocoa, weakly raphanoid, strongly raphanoid, earthy, fruit or soap; taste often mild, occasionally raphanoid, rarely bitter, weakly bitter or weakly raphanoid where recorded.

  Spore deposit colour: usually brownish olive, occasionally yellowish brown.

  Exsiccata characters: occasionally pale, rarely fragile or shiny.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, occasionally limoniform, rarely ovoid, fusoid or cylindrical; colour in microscope occasionally brown, yellow brown or yellow, rarely brown yellow, grey yellow or very pale; guttules variable rarely weak. papilla variable occasionally weak, rarely very strongly; Spore Code: (O2) O3; (P0) P1; (D0) D1 D2.

  Basidia: (20) 23–39 (42) x 6–11 μm; ave. Q 2.9–4.6; spore arrangement 4 spored;

  Cheilocystidia: main shape usually clavate-stipitate, often capitate-stipitate, occasionally spathulate-stipitate, rarely clavate-lageniform or clavate-ventricose, clavate, capitate, gently clavate or subcapitate; special features observed occasionally conglutinate, apical thickening, sinuate or septa, rarely median thickening, bifurcate, geniculate, yellow contents, branching, clamped septa, irregular, many collapsed in exsiccata, mucous, thick content in neck or uniform; cheilocystidia ratios: A/M = 1.72–3.16; A/B = 1.16–4.24; B/M = 0.76–1.58.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 120 μm; ixocutis hyphae width up to 8 μm; ixocutis hyphae encrustation usually yes, occasionally no; shape of trama elements beneath subcutis thickly sausage-shaped, usually cylindrical, occasionally ellipsoid, angular or isodiametric, rarely spherical up to 19 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 120 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Where only one possible associate was recorded, the most commonly recorded associate was Populus (23.2%) but Salix (18.2%), Picea (14.1%), Pinus (10.1%), Betula (10.1%), Tilia (9.1%), Quercus (5.0%), Carpinus (2.0%), Fagus (2.0%), Cedrus (2.0%), Helianthemum (1.0%), Castanea (1.0%), Abies (1.0%) and Tsuga (1.0%) were also recorded. In these cases the most commonly recorded families were Salicaceae (42.5%), Pinaceae (30.8%), Betulaceae (10.8%), Malvaceae (7.5%) and Fagaceae (7.5%). We have additional records where Alnus (8.2%), Larix (2.6%), Corylus (1.0%) and Pseudotsuga (1.0%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Salicaceae (51.0%), Pinaceae (41.2%), Betulaceae (31.4%), Fagaceae (12.9%) and Malvaceae (5.2%) The growth habit of our collections was often scattered, occasionally gregarious or solitary and rarely caespitose.

  According to our current data, the species is found on multiple continents with collections found in Northern America (53.7%), Europe (44.0%), Temperate Asia (1.3%) and Africa (0.9%). 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. temperate broadleaf & mixed forests (42.0%) and boreal forests/taiga (26.1%), specifically including the ecoregions: Watson Highlands taiga (11.5%). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (32.6%), 1.1 Forest – Boreal (17.7%) and 14.5 Urban Areas (15.5%) 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 Subarctic America (Yukon, Alaska, Northwest Territories, Greenland and Nunavut), Eastern Canada (Quebec and Newfoundland and Labrador), Northwestern U.S.A. (Colorado, Washington and Oregon), Mexico (Mexico), Western Canada (British Columbia, Alberta and Saskatchewan), Northeastern U.S.A. (Michigan), North-central U.S.A. (Wisconsin and Missouri) and Southeastern U.S.A. (Maryland).

  Within Europe we have records from the Centre (Germany, Poland, Belgium, Netherlands, Czech Republic, Switzerland, Hungary and Austria), the Southeast (North Macedonia and Italy), the Southwest (France and Spain), the North (England, Denmark, Sweden, Finland and Norway) and Eastern Europe (Estonia and Lithuania). Specimens have been collected from 41.0°N to 66.9°N.

  Within Temperate Asia we have records from Eastern Asia (Japan), Western Asia (Turkey) and China (Sichuan).

  Within Africa all our records are from Northern Africa (Morocco).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma eburneum is monophyletic but not supported by bootstrap ≥ 80% (75%) in the results of five or six locus analyses. If species identification is to be achieved with a single locus, then RPB2 is the best candidate among the loci tested. Used in combination, V6 and V9 should also be efficient, as the H. eburneum V6 clusters with H. aanenii and V9 with H. alpinum. In many cases, the species cannot be identified by ITS. Synonymizations of H. albocolossum, H. crustuliniforme var. tiliae, H. ochroalbidum and H. perpallidum are supported by molecular data.

• arrow_drop_downarrow_drop_upCommentary
  Given the shape of its cheilocystidia, Hebeloma eburneum clearly belongs to H. subsect. Crustuliniformia. This species most likely corresponds to ICG3 of Aanen & Kuyper (1999). It appears to have a wide range both geographically and ecologically. There is no morphological or molecular evidence to separate this species from H. albocolossum, H. ochroalbidum and H. perpallidum, which were all described as large and fleshy with a very pale coloured pileus. Moser saw the primary differences as being the presence or absence of tears on the lamellae and the discolouration of the stipe. He regarded H. eburneum as a Mediterranean species and the others as more northern. He also believed spore size and the presence of a papilla on the spores, leading to a more limoniform shape, as significant. The presence or absence of tears can be affected by the weather and, while it is a good character, it is not a dependable character. The discolouration of the stipe is also an important character, but again can be affected by local ecology; for this species, the stipe does not usually discolour very much with age, however, when conditions are very damp the stipe can exhibit some discolouring, which starts from the base of the stipe. With regard to the spore papilla, in our experience this species does sometimes have some spores with a papilla, but it is rarely strong and so spores with a limoniform shape are not common. This species is a member of what we call the alpinum-complex, along with H. aanenii, H. alpinum, H. crustuliniforme and H. geminatum. It is morphologically close to H. aanenii and to H. geminatum, but it usually has rather larger spores; we have had two collections of H. eburneum that have had smaller spores than usual and if the spores are both short and narrow it may become difficult to separate these species. This species is also similar to. crustuliniforme, but can be distinguished through its cheilocystidia which have on average a larger apex. Hebeloma crustuliniforme also tends to have a rather more coloured pileus. Hebeloma alpinum only occurs in alpine or arctic habitats, where we have never found H. eburneum. An unusual feature of this taxon is the huge range in the number of full length lamellae (L). We give the range above as 40–110. As a result, we have to key this taxon out twice in the key to this section. It is very unusual to have a species of Hebeloma with such a wide range for this value L and, as a result, we did explore the possibility that there may be more than one species involved. However, ecologically, molecularly and morphologically (apart from the L value) we have found no further evidence to support more than one species. We discussed in Eberhardt et al. (2015a) the difficulty in resolving which of the synonyms mentioned above had priority. It appears strange that such a distinctive mushroom was not described until 1970 and then described several times within a few years. In fact, it was probably often confused with (and recorded as) H. crustuliniforme. Further, we do mention a number of names that probably do refer to members of this complex, but without original material it is not possible to determine, without ambiguity, to which mushrooms they should be referred.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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