Hebeloma marginatulum (J. Favre) Bruchet, Bull. Mens. Soc. Linn. Lyon 39 (6, suppl.): 43 (1970)

Cripps, Cathy L., Eberhardt, Ursula, Schuetz, Nicole, Beker, Henry J., Vera S. Evenson, & Horak, Egon, 2019, The genus Hebeloma in the Rocky Mountain Alpine Zone, MycoKeys 46, pp. 1-54 : 25-28

8. Hebeloma marginatulum (J. Favre) Bruchet, Bull. Mens. Soc. Linn. Lyon 39 (6, suppl.): 43 (1970) Figures 6B, 14, 23 (8)

Etymology.

From marginatus, with a margin or border, emphasizing a thin line of tissue near the margin.

Description.

Cortina present, remnants distinctly present in some. Pileus 15 –40(– 50) mm in diameter, slightly conic-convex, domed convex, irregular, sometimes with a flat center that can even be dished, smooth or rough due to velipellus, shiny, strongly canescent, underneath dark brown, dark chestnut, to dark caramel color, mostly uniform but two-toned in some and then lighter at margin (more hoary, dingy whitish, or ochraceous in one), with a fine white border around the pileus perimeter a few mm in from margin, not hygrophanous; margin turned down or in, rather persistently so, and then covered with copious veil, often irregular, wavy, fragile. In one collection, the cuticle is rather thick and rubbery. Lamellae deeply emarginate and squared off, some pulling away, somewhat broad, L = 30-40 plus lamellulae, cream, then pinkish buff, darkening to medium coffee brown; edges fimbriate. Stipe 20 –40(– 45) mm × 2 –6(– 10) mm, equal, undulating or not, pale buff (some with possible yellow tint), and dark (up to black) at base, pruinose at apex, longitudinally fibrous lower, with a few longitudinal fibrils. Context dingy whitish, some with yellowish tones and dark at base. Odor raphanoid or sourish, sometimes faint. Exsiccate: pileus pale brown to dark brown, some obviously canescent; lamellae medium brown; stipe buff or ocher, darker at base.

Basidiospores yellowish gray, pale in Melzers, elliptical with rounded end, inequilateral in side view, no big apiculus, not guttulate, smooth to slightly punctate or rough (O1, O2), indextrinoid (D0, D1), perispore not loosening (P0), 9 –12(– 13) × 5.5 –7(– 8) µm, on average 10.1 × 6.4 µm, Q = 1.59. Basidia 25-35 × 8-9 µm, clavate, two and four-spored. Cheilocystidia lageniform, ventricose, often with very long equal neck, and somewhat gradually swollen base, occasionally clavate at apex, sometimes cylindrical, 35-80 µm long × 4-7 µm at apex, 4-6 in middle, and 7-12 (13) at base, no thickening noticed. Pleurocystidia absent. Epicutis thickness 40-100 µm, with some encrusted hyphae.

Rocky Mountain ecology.

In the Rocky Mountain alpine zone, with various willows, including dwarf willows Salix arctica and S. reticulata , and shrub willow S. planifolia . Known from both Colorado and Montana.

Rocky Mountain specimens examined.

U.S.A. COLORADO: Front Range, Loveland Pass, 12 Aug 2013, in Dryas , DBG-F-027694, C. Cripps; 12 Aug 2013, with Salix sp., DBG-F-027695, C. Cripps; 25 Aug 2000, with Salix sp., DBG-F-020708, V.S. Evenson; 21 Aug 2003, with Salix sp., DBG-F-021388, V.S. Evenson; 20 Aug 2013, DBG-F-027682, L. Gillman; 21 Aug 2003, with Salix sp., DBG-F-021405, O.K. Miller, Jr; San Juan County, Cinnamon Pass, 3700 m, with Salix arctica , 29 July 2000, CLC 1413 (MONT), C. Cripps, 3700 m, with Salix arctica , 27 July 2002, CLC1811 (MONT), C. Cripps; 29 July 2000, with S. reticulata and Salix sp., ZT9002 (ETH), E. Horak; Black Bear Basin, 2 Aug 2000, 3830 m, with S. planifolia , CLC1448 (MONT), C. Cripps; 8 Aug 2000, with S. arctica , CLC1449 (MONT), C. Cripps; 11 Aug 2001, with S. reticulata , ZT9813 (ETH), E. Horak; 3760 m, with Salix arctica , 11 Aug 2001, CLC1718 (MONT), C. Cripps; Emma Lake/Horseshoe Basin, 3688 m, with S. arctica , 31 July 2002, CLC1874 (MONT), C. Cripps; 31 July 2002, with S. arctica , CLC1880 (MONT), C. Cripps; Imogene Pass, 29 July 2002, 3850 m, with S. arctica , CLC1836 (MONT), C. Cripps; Mineral Basin, 3850 m, with S. arctica , 29 July 2002, with S. arctica , CLC1840 (MONT), C. Cripps; without obvious host, although Salix in the vicinity, 30 July 2002, CLC1860 (MONT), C. Cripps; with S. arctica and S. planifolia , 30 July 2002, CLC1861 (MONT), C. Cripps; 3835 m, with S. arctica , 7 Aug 2001, CLC1667 (MONT), C. Cripps; Stony Pass, 3840 m, with S. arctica , 28 July 2002, CLC1824 (MONT), C. Cripps; 3840 m, with S. arctica , 28 July 2002, CLC1826 (MONT), C. Cripps. Sawatch Range, Independence, 3 Aug 2000, with Salix sp., DBG-F-020841, DBG-F-020856, V.S. Evenson; 3 Aug 2000 with Salix sp., DBG-F-020843, V.S. Evenson; 3760 m, with S. planifolia , 7 Aug 2000, CLC1478 (MONT), C. Cripps. MONTANA: Carbon County, Beartooth Plateau, site 1, 9 Sept 2000, with S. planifolia , CLC1545 (MONT), C. Cripps; Quad Creek, 8 Aug 2008, with S. planifolia , HJB12458, A. and M. Ronikier; 11 Aug 2017; with Salix reticulata and S. planifolia , 11 Aug 2017, CLC3545 (MONT), C. Cripps.

Discussion.

Hebeloma marginatulum is distinct from other species of the H. mesophaeum complex, but not by much as to molecular distance (Fig. 6B). The species is paraphyletic in relation to the monophylum including the other taxa of the complex. With 0-19 [0-2] bp, the intraspecific variation is quite extensive in H. marginatulum in terms of total differences. Within each dataset, the ITS variation is also quite large, 0-14 [0-2] bp for the RM (29 sequences) and 0-17 [0-2] bp for the FE dataset (21 sequences). However, the total number of considered sequences is also larger than for other species.

This taxon was first described as H. versipelle var. marginatulum by Favre (1955) from the alpine region of the Swiss Alps and was later raised to species level by Bruchet (1970). It is now considered to be restricted to arctic and alpine habitats primarily with dwarf willows ( Beker et al. 2016, 2018). Confirmed records show it to be present in these habitats in Canada, Greenland, Iceland, Scandinavia, Svalbard as well as the European Alps and the Carpathians and Rocky Mountains ( Eberhardt et al. 2015b; Beker et al. 2016). Vesterholt (2005) described H. polare as a darker brown closely related species, but this has been synonymized with H. marginatulum ( Beker et al. 2016). The Rocky Mountain specimens are also mostly uniformly dark brown with a canescent sheen.

Collections from the alpine that are very hoary and dark brown have been misinterpreted as H. bruchetii Bon ( Miller and Evenson 2001) before molecular techniques; H. bruchetii , first described as an alpine species, has now been synonymized with H. mesophaeum and should have smaller spores. Hebeloma marginatulum is mentioned as a subalpine species (in Idaho) by Smith et al. (1983) who described two varieties (ver. fallax , var. proximum ) from the subalpine in Colorado. Smith’s spore descriptions (dextrinoid with sharp ends) for his varieties may not fit this species, but the authors recognize that these varieties of H. marginatulum , and indeed other closely related species, need more study in North America.

This species is in H. sect. Hebeloma because of basidiomes with a cortina and the ventricose cheilocystidia together with the non-dextrinoid, or barely dextrinoid, spores that are primarily elliptical; within this group, it has an arctic-alpine habitat and relatively large spores (greater than 10 × 6 µm).