Hebeloma ischnostylum (Photo: H. J. Beker)

Taxonomy

Basionym:
Agaricus ischnostylus Cooke, Grevillea 12 (64): 98 (1884)

Types: Cooke`s Library, Cooke’s Original Plates. unpublished, Royal Botanical Gardens Kew, London: 802 (1891-1911) pl. 894, lectotype (icon) designated by Beker et al., Hebeloma (Fr.) P. Kumm.: (2016) page 514 (MBT203466) FRANCE: Alpes-Maritimes, Les Espagnols (43.5089°N, 6.7935°E, alt. approx. 200 m a.s.l.) on bare soil in mixed woodland under Populus sp. and Salix sp., 16 Oct. 2007, R. Newton (Epitype. herbarium acc. no. BR 5020184123505, HJB12116). Epitype designated by Beker et al., Hebeloma (Fr.) P. Kumm.: (2016) page 514 (MBT203467).

• arrow_drop_downarrow_drop_upType notes
  The lectotype (icon) was a collection from ENGLAND: Shropshire, Shrewsbury on grassy ground under Alnus glutinosa, Sep. 1879, (K(M). This is Cooke’s original hand-coloured illustration no. 894), elements from which were later published as Plate 420 in Cooke (Illustr. Brit. Fungi (1884) [“1881–1891”])

Heterotypic synonyms:

• Hebeloma fragrantissimum Velen., Ceske Houby: 395 (1919) ["1920"]
• Hebeloma laevatum (Britzelm.) Sacc., Syll. Fung. 11 (1-7): 55 (1895)
• Agaricus laevatus Britzelm. ., Botanisches Centralblatt 54 (15-17): 68 (1893)

Homotypic synonyms:

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

• arrow_drop_downarrow_drop_upEtymology
  From ischno– thin and stylos– a pillar, emphasizing the slenderness of the stipe.

• arrow_drop_downarrow_drop_upDiagnosis
  Pileus slightly viscid, smooth, even, convex, then expanded, and broadly umbonate, white or a little pallid at the disc, inodorous (or with a faint odour of Spirea), margin thin, stem slender, equal, or a little thickened at the base, solid, smooth, naked, gills rounded behind and adnate, slightly serrate at the margin, whitish then argillaceous. On the ground, amongst grass. Shrewsbury. Pileus 1–2 inches [2.5–5 cm] broad, stem 2 inches [5 cm] long, 1/8 to 1/6 ins [3–4 mm] thick, allied to Ag. nudipes, but evidently not any form of that species. Will be figured in the “Illustrations”.

Description

Description of Hebeloma ischnostylum based on 40 collections

• arrow_drop_downarrow_drop_upMacroscopic description
  Pileus: (11) 14–46 (85) mm diameter; shape occasionally convex, umbonate or broadly umbonate, rarely strongly umbonate; characters occasionally rimulose or tomentose, rarely hygrophanous, pubescent, spotting or squamulose; margin characters often involute or smooth, rarely fibrillose or ribbed; viscosity tacky when moist; colour variation usually unicolour, rarely two color; colour at centre occasionally cream, pale cream or pale yellow.

  Lamellae: attachment often adnate or emarginate, occasionally decurrent tooth, rarely adnexed or free; maximum depth 4–8 mm; number of complete lamellae 31–60; presence of tears often absent, occasionally visible with x10 lens, rarely visible with naked eye; white fimbriate edge often present, occasionally absent or weak, rarely very strong.

  Cortina presence: no.

  Stipe: (12) 28–47 (65) x 3–6 (8) {median} x 3–9 (11) {basal} mm; stipe Q 4.2–17.3; base shape usually cylindrical, often clavate; floccosity occasionally fibrillose, floccose, pruinose or pruinose at apex, rarely floccose at apex, weakly floccose or velute; rooting usually no, rarely yes; thick rhizoids at base usually absent, rarely present;

  Context: Texture firm; stipe interior usually hollow, often stuffed; stipe flesh discolouring variable occasionally weak; slenderness measure 4.7–17.6; smell sacchariolentia, often sweet, rarely cocoa; taste mild where recorded.

  Spore deposit colour: often brownish olive, occasionally yellowish brown or cinnamon.

  Exsiccata characters: occasionally stipe blackening, pale or pileus blackening, rarely lamellae blackening.

• arrow_drop_downarrow_drop_upMicroscopic description
  Spores: shape usually amygdaloid, often fusoid, occasionally limoniform; colour in microscope often brown, occasionally yellow or yellow brown; guttules usually yes, occasionally no. papilla variable often weak; Spore Code: O3 (O4); P2 P3; D3 (D4).

  Basidia: (27) 29–42 (43) x 6–8 (9) μm; ave. Q 3.7–5.6; spore arrangement usually 4 spored, rarely variable;

  Cheilocystidia: main shape often gently clavate or cylindrical, occasionally clavate, rarely balloon-shaped, clavate-stipitate, clavate-lageniform or clavate-ventricose, tapering, filiform or ventricose; special features observed occasionally septa, clamped septa or irregular, rarely bifurcate, yellow contents, apical thickening, grotesque, many collapsed in exsiccata, mucronate, rostrate or sinuate; cheilocystidia ratios: A/M = 1.03–1.66; A/B = 1.19–2.21; B/M = 0.76–1.11.

  Pleurocystidia: none seen.

  Ixocutis: epicutis thickness (measured from exsiccata) up to 185 μm; ixocutis hyphae width up to 6 μm; ixocutis hyphae encrustation variable; shape of trama elements beneath subcutis often ellipsoid, occasionally cylindrical, thickly sausage-shaped or spherical up to 25 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
  Hebeloma ischnostylum's preferred habitat appears to be mixed woodland with grassy soil. Where only one possible associate was recorded, the most commonly recorded associate was Quercus (46.1%) but Alnus (15.4%), Tilia (15.4%), Salix (15.4%) and Populus (7.7%) were also recorded. In these cases the most commonly recorded families were Fagaceae (41.2%), Salicaceae (29.4%), Betulaceae (11.8%), Malvaceae (11.8%) and Pinaceae (5.9%). We have additional records where Picea (18.8%), Betula (15.6%), Carpinus (12.5%), Fagus (6.2%), Pinus (6.2%), Corylus (3.1%) and Larix (3.1%) were recorded as possible associates, but in these cases a number of possible associates were mentioned. Overall the most commonly recorded families are Betulaceae (40.6%), Salicaceae (40.6%), Fagaceae (34.4%), Pinaceae (21.9%) and Malvaceae (6.2%) The growth habit of our collections was often scattered, occasionally caespitose or gregarious and rarely solitary.

  According to our current data, the species is found on multiple continents with collections found in Europe (64.1%) and Northern America (35.9%). 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 (65.8%), mediterranean forests, woodlands & scrub (13.2%) and temperate conifer forests (13.2%), specifically including the ecoregions: Northeast Spain and Southern France Mediterranean forests (10.5%) and Appalachian-Blue Ridge forests (10.5%). From collector information, it appears collections have been found in the 1.4 Forest – Temperate (55.6%) and 14.5 Urban Areas (33.3%) 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 (England, Denmark, Norway, Finland and Sweden), the Southwest (France and Spain), the Centre (Germany, Belgium and Czech Republic) and the Southeast (Italy). Specimens have been collected from 41.8°N to 61.8°N.

  Within Northern America we have records from Northeastern U.S.A. (New York, Pennsylvania and Ohio), Northwestern U.S.A. (Oregon and Washington), Western Canada (British Columbia) and Eastern Canada (Quebec).

• arrow_drop_downarrow_drop_upMolecular results
  See H. fusisporum. Hebeloma ischnostylum is well supported by the mitochondrial loci and Tef1a.

• arrow_drop_downarrow_drop_upCommentary
  The smell associated with Hebeloma ischnostylum immediately places it in H. sect. Sacchariolentia. The spore width, on average less then than 7 μm, means it can only be H. sacchariolens, H. fusisporum or H. ischnostylum. Both H. fusisporum and H. ischnostylum have fusoid spores (Q > 1.8) and a pileus colour that is always white to ivory (other than through ageing); H. sacchariolens has average spore Q less than 1.8 and is usually two-coloured with brownish tones in the centre. Hebeloma fusisporum has somewhat bigger spores than H. ischnostylum, both in width and length (and indeed spore Q value although here there is some overlap). Also, H. ischnostylum is generally less slender than H. fusisporum. We should mention the difficulty in measuring the spores of this taxon; with the perispore strongly loosening in many spores it is easy to overestimate the width of the spores by failing to exclude the loosening perispore from the measurement. Hebeloma ischnostylum can occasionally have a tomentose or cracking pileus which leads to confusion with H. odoratissimum, but these two taxa can be readily separated on both macroscopic and microscopic characters. For H. ischnostylum, the tomentum rarely persists and disappears with age. Hebeloma ischnostylum often has drops on the lamellae edges; it also has the most defined cheilocystidia of any taxon within this section and they are usually easy to find. While the lamella edge is not completely sterile, it does appear to have sterile areas along its edge where the cheilocystidia are clearly packed together. In his description of H. ischnostylum, Cooke specifically mentions the smell like “Spirea ulmaria” (Filipendula ulmaria), that it was collected with Alnus glutinosa, the whitish colour of the pileus and the slender stipe. He gives spore dimensions as approx. 12 × 7 μm, but in his drawing they are much more fusoid than this would suggest. We have measured the spores in his drawing, and if we assume the average length is 12 μm then the width is 5.8 μm and the Q value is 2.1. We have searched extensively, particularly at K, for any original material but failed to locate any. Nonetheless, we are satisfied that this is the correct name for this taxon, for which we have a number of collections from England. Other synonyms of this species are H. fragrantissimum and H. laevatum. The type of the former was stored in a bottle of ethanol/ formaldehyde at PRC. Although we have not been able to amplify DNA, we have been able to make a morphological analysis based on the macroscopic description of Velenovsky (1920) and our microscopic observations. It is clearly a member of H. sect. Sacchariolentia. Being described with a white pileus, breaking up into small scales with age, and a 3–4 mm broad stipe, it agrees best with H. ischnostylum. Average spore parameters from the holotype (11 × 5.9 μm) rule out H. fusisporum, but do fall within the range of H. ischnostylum and additionally the average spore Q (1.87) would support this identification. Interestingly, Velenovsky estimated the spore length to be in the range 14–16 μm; we do not know exactly the effects of the medium within which this collection has been stored. We conclude that H. fragrantissimum is a synonym of H. ischnostylum. Agaricus laevatus is described and illustrated with a matt pileus becoming scaly, a tapering stipe, an almost pleasant smell, spores of 9–11 × 5 μm, growing in heathland. In Hebeloma, a matt and scaly pileus is known from H. odoratissimum, H. ischnostylum and H. fusisporum, three species that may also be interpreted as having a pleasant smell. Hebeloma odoratissimum has much broader spores and is not likely to occur in heathland. Hebeloma fusisporum has larger spores. Hebeloma ischnostylum may occur with Salix on poor soil and the icon showing the very pale pileus makes it very likely to be this species. We therefore synonymize H. laevatum with H. ischnostylum.

Geographic distribution

Phenology

• arrow_drop_downarrow_drop_upAdditional cited collections

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