Hebeloma nanum (Photo: K. Kokkonen)

Taxonomy

Types: CZECH REPUBLIC: Bohemia, SE of Prague, Mirosovice, Mnichovice (approx. 49.9349°N, 14.7097°E, alt. approx. 355 m a.s.l.) in dry woodland under Picea sp., 20 Jun. 1936, J. Velenovsky (Holotype. herbarium acc. no. PRM153761, HJB1000155).

Heterotypic synonyms:

• Hebeloma sordidum var. microsporum Saini & Atri, Geobios New Reports 4: 2 (1985)
• Hebeloma crustuliniforme f. microspermum Hongo, J. Jap. Bot. 41 (6): 169 (1966)

• arrow_drop_downarrow_drop_upEtymology
  From nanus– dwarf, presumably to emphasise the small size of the basidiomes, except they are actually not that small, even Velenovsky gives the pileus as 3–4 cm diameter. Perhaps he had a different character in mind that he was describing as small, for example the stipe?

• arrow_drop_downarrow_drop_upOriginal diagnosis
  H. nanum sp. n. Fasciculatum, 3–5 cephalum. Carnosum, pil. 3–4 cm, cito explanato, obtuse leniter umbonato, glabro, nitenti, udo viscoso, non hygroph., sordide pallescenti, centro ochraceo. St. p. r. aequans, 8–10 mm. cr., rigide solidus, pure albus, totus (!) granuloso-squamosus. Lam. confertae, angustae, postice attenuatae, argillaceae. Sp. Fusoideae (!), pallide fulvae 6–9. Cyst. filiformia, recta, obtusa, septata 25. Caro olida. In piceto arido pr. Mnichovice 6, 1926. Affine praecedenti (H. octavii), equidem vernali. Stipite duro brevi insigne.

• arrow_drop_downarrow_drop_upEnglish translation
  Hebeloma nanum sp. nov. Fasciculate, 3–5 together. Fleshy, pileus 3–4 cm, quickly expanding, bluntly and slightly umbonate, shiny, viscous when moist, not hygrophanous, sordid, pallescent, ochraceous at centre. Stipe equal, 8–10 mm broad, stiff, solid, purely white, entirely granulose-squamulose. Lamellae crowded, narrow, attenuate towards end, clay-coloured. Spores fusiform, pale yellow, 6–9 μm. Cystidia filiform, straight, blunt, septate, 25 μm. Context with unpleasant smell. In dry Picea forest near Mnichovice, June 1926. Close to the former species (H. octavii), equally vernal. Distinguished by the short, hard stipe.

Description

Description of Hebeloma nanum based on 44 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (13) 15–58 (72) mm diameter; shape often convex, occasionally strongly umbonate, rarely broadly umbonate, umbonate, umbilicate or weakly umbonate; characters occasionally spotting, rarely hygrophanous or remains of universal veil; margin characters often smooth, rarely involute, eroded, crenulate, fibrillose, reflexed, scalloped, sulcate or wavy; viscosity tacky when moist; colour variation usually unicolour, rarely two color; colour at centre occasionally dark pinkish buff or ochraceous, rarely clay-buff, yellowish brown, pale cream, cream, cinnamon, pale pinkish buff or dark greyish buff.

  Lamellae: attachment usually emarginate, rarely adnexed, adnate or decurrent tooth; maximum depth 1–7 mm; number of complete lamellae 48–108; presence of tears usually absent, rarely visible with naked eye or visible with x10 lens; white fimbriate edge often weak, occasionally present, rarely absent or very strong.

  Cortina presence: usually no, rarely yes.

  Stipe: (13) 17–51 (60) x 3–14 (18) {median} x 3–13 (19) {basal} mm; stipe Q 2.0–8.1; base shape often cylindrical, occasionally tapering, rarely clavate or subbulbous; floccosity occasionally fibrillose, pruinose at apex or floccose, rarely pruinose, velute, transverse or floccose at apex; rooting often no, occasionally yes; thick rhizoids at base absent;

  Context: Texture firm; stipe interior often stuffed or hollow, rarely superior wick; stipe flesh discolouring often no, occasionally yes, rarely weak; slenderness measure 1.6–14.5; smell occasionally raphanoid or cocoa, rarely odourless, fruit, strongly raphanoid or soap; taste often mild, occasionally weakly bitter or none where recorded.

  Spore deposit colour: often brownish olive, rarely clay-buff, umber or greyish brown.

  Exsiccata characters: rarely pale or pileus blackening.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape amygdaloid, occasionally fusoid or limoniform; colour in microscope often yellow, rarely brown, yellow pale or brown pale; guttules often yes, occasionally no. papilla variable occasionally weak; Spore Code: O1 O2; P0 P1 (P2); (D1) D2 D3.

  Basidia: (15) 16–32 x (4) 5–8 μm; ave. Q 3.1–4.1; spore arrangement 4 spored;

  Cheilocystidia: main shape usually cylindrical, occasionally clavate, clavate-lageniform or clavate-ventricose or gently clavate, rarely ventricose, clavate-stipitate, filiform, lageniform or utriform; special features observed often septa, occasionally short, irregular, bifurcate, branching or rostrate, rarely many collapsed in exsiccata, geniculate, clamped septa, conglutinate, mucronate or sparse; cheilocystidia ratios: A/M = 1.01–1.47; A/B = 0.95–1.54; B/M = 0.83–1.18.

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

  Ixocutis: epicutis thickness (measured from exsiccata) up to 120 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation often yes, occasionally no; shape of trama elements beneath subcutis thinly sausage-shaped, often thickly sausage-shaped, occasionally ellipsoid or isodiametric up to 20 μm wide.

  Caulocystidia: Similar to cheilocystidia but larger, up to 110 μm.

• arrow_drop_downarrow_drop_upSpore measurements

• arrow_drop_downarrow_drop_upCheilocystidia measurements

• arrow_drop_downarrow_drop_upHabitat and distribution
  Hebeloma nanum's preferred habitat appears to be coniferous woodland. Where only one possible associate was recorded, the most commonly recorded associate was Pinus (68.2%) but Picea (9.1%), Cedrus (9.1%), Betula (9.1%) and Castanea (4.5%) were also recorded. In these cases the most commonly recorded families were Pinaceae (87.5%) and Betulaceae (8.3%). We have additional records where Populus (7.3%), Quercus (4.9%), Arctostaphylos (2.4%), Larix (2.4%), Salix (2.4%) and Eucalyptus (2.4%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Pinaceae (87.8%), Betulaceae (36.6%), Salicaceae (7.3%) and Fagaceae (7.3%) 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 Northern America (45.2%), Europe (42.9%), Temperate Asia (7.1%) and Tropical Asia (4.8%). 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. boreal forests/taiga (43.9%) and temperate broadleaf & mixed forests (43.9%), specifically including the ecoregions: Northern Canadian Shield taiga (29.3%) and Central European mixed forests (22.0%). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (40.0%), 1.1 Forest – Boreal (30.0%) and 3.3 Shrubland – Boreal (17.5%) 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 (Northwest Territories, Nunavut and Alaska) and Southeastern U.S.A. (Tennessee).

  Within Europe we have records from the Centre (Poland, Germany and Czech Republic), the North (Finland, Scotland and England), the Southwest (Italy and Spain) and the Southeast (Italy). Specimens have been collected from 41.8°N to 68.2°N.

  Within Temperate Asia we have records from Eastern Asia (Japan) and China (Yunnan).

  Within Tropical Asia all our records are from Indian Subcontinent (India).

• arrow_drop_downarrow_drop_upMolecular results
  Hebeloma nanum is well supported in the five-locus phylogeny and by nuclear loci, but the species appears to have two different variants of mitochondrial SSU. The V6 and V9 sequences of some collections of H. nanum cluster together with H. catalaunicum, whereas the majority is included in a sisterclade in V9 and in a sisterclade with H. naviculosporum in V6. Collections from a small area in Poland are present in both subgroups. There is a subclade in the ITS tree that almost, but not entirely, coincides with the H. nanum collections clustering with H. catalaunicum in the mitochondrial loci. The protein-coding loci do not support this split at all. We got the ITS and V6 sequences of the type of H. nanum and it is in the majority group of H. nanum, but we do not have the V9 sequence of the type of H. nanum. However, in the absence of conclusive molecular data and with no indication in morphology for a possible split, we rather treat H. nanum as a single taxon. We are not aware of any ITS sequence from outside Europe that is likely to belong to this species, although similar sequences have been published from Alaska.

• arrow_drop_downarrow_drop_upCommentary
  Hebeloma nanum is macroscopically a very distinctive Hebeloma. In the field it is the colour of the pileus that is the most remarkable feature; an orange brown colour that appears to be confined, in Europe, to this species and the closely related H. catalaunicum and H. naviculosporum. While the colour of the pileus appears to be a consistent character, it can fade with time and may only be obvious in young specimens. Microscopically the fusoid spores with Q value greater than 1.8 is also a good character. The narrow, mostly O2, spores (at most 5 μm wide on average) together with the pileus colour and the large number of lamellae (L greater than 65), separate this taxon from other of H. sects. Scabrispora and Naviculospora. The cheilocystidia of this species are problematic (as they are for H. naviculosporum); they are primarily cylindrically shaped but a number can also appear gently clavate. If one focuses on the gently clavate cheilocystidia it is apparent that they are much shorter and less clavate than one would expect from species of H. sect. Velutipes. The cylindrical cystidia suggest to place this taxon in H. sect. Scabrispora and, indeed, it does appear to be quite closely related, but our phylogenetic results do indicate otherwise, as discussed above. Hebeloma nanum was described by Velenovsky (1939), but it has rarely been recorded since and has been overlooked in much of the literature.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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