Hebeloma nigellum Bruchet, Bull. Mens. Soc. Linn. Lyon 39 (6 suppl.): 126 (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 : 39

15. Hebeloma nigellum Bruchet, Bull. Mens. Soc. Linn. Lyon 39 (6 suppl.): 126 (1970) Figures 6A, 21, 23 (15)

Etymology.

From nigellus, meaning blackish for the dark pileus.

Description.

Cortina present. Pileus 8-20 mm in diameter, broadly convex to hemispherical to almost plane with a small umbo, greasy, smooth or slightly fibrous, in center dark date brown, chocolate brown, or blackish brown, at margin paler even to cream, appearing two-toned, with hoary sheen, glazed-looking, not hygrophanous; margin inrolled at first, then even (not rimose). Lamellae emarginate, even with a tooth, normally spaced, L = 24-32 with lamellulae, whitish, then pale milk coffee, pale brown, paleness persisting; edges floccose. Stipe 15-50 × 1.5-4 mm, long and slim, equal, undulating a bit, pale dingy whitish in top half darkening to black brown at base, pruinose at apex, below silky-shiny, smooth to fibrillose. Context dingy whitish, darkening to brownish at base, rubbery in stipe. Odor raphanoid. Exsiccate: pileus small, two-toned, center dark brown, outwards cream; lamellae brown, red-brown; stipe long and very thin, cream, dark at base.

Basidiospores yellowish brown, amygdaliform, a few ellipsoid in certain view, no/slight snout, no big apiculus, slightly rough (O1, O2), perispore occasionally observed loosening very slightly (P0, P1), usually distinctly dextrinoid (D2, D3), not guttulate, 10-14.5 × 6-8 µm, on average 11.9 × 7.2 µm, Q = 1.6. Basidia 27-40 × 7.58-10.5 µm, sterigma 2-3 µm, clavate, mainly four-spored. Cheilocystidia lageniform, more or less swollen at the base, top half cylindrical, some apical thickening, some septate, 30-80 × 3.5-6.5 µm at apex, 3.5-6 µm in middle, 6.5-12.5 µm at base. Pleurocystidia absent. Epicutis thickness 40-75 µm, with no encrusted hyphae recorded.

Rocky Mountain ecology.

Alpine mostly near Salix planifolia and in moss; reported from Colorado and Montana.

Rocky Mountain specimens examined.

U.S.A. COLORADO: San Juan County, San Juan Mountains, Engineer Pass, in Salix planifolia , 30 July 2000, CLC1420 (MONT), C. Cripps; Cinnamon Pass, in Salix spp., 10 Aug 2001, CLC1707 (MONT), C. Cripps. MONTANA: Beartooth Plateau, Frozen Lakes: at 3200 m in moss near S. planifolia , 21 Aug 2001, CLC1778 (MONT), C. Cripps; N Pass, with S. planifolia , 9 Aug 1998, ZT6425 (ETH), E. Horak; Billings Fen, in moss near S. planifolia , 23 Aug 2017, CLC3614b (MONT), C. Cripps.

Discussion.

According to Beker et al. (2016), H. nigellum is paraphyletic in the ITS region, but monophyletic and bootstrap supported in multi-locus analyses. The corresponding network is in Figure 6A. Hebeloma nigellum is similar in its variabiltiy within the Rocky Mountains (1-7 [0-1] bp differences based on 5 sequences when compared with the random selection of 11 sequences from the FE dataset (0-8 [0-3] bp). As discussed above, H. nigellum is close to and not always distinguishable from H. hygrophilum by ITS sequence. Another arctic and alpine species is H. spetsbergense (discussed below) that cannot be distinguished from H. nigellum by ITS sequence either.

Hebeloma nigellum is a small, slim species with a dark-centered pileus and rather large, dextrinoid, amygdaliform spores. It is widespread across northern Europe, not only in arctic-alpine habitats, and is reported from alpine and arctic habitats in Canada, Greenland, Iceland, Svalbard and the European Alps ( Beker et al. 2016, 2018). In molecular and morphological features it is close to H. hygrophilum (which normally associates with Salix in non-arctic-alpine habitats). Hebeloma kuehneri Bruchet, a commonly reported arctic-alpine species, was described in the same paper as H. nigellum with the main differentiation being that the former has more brownish coloration and the latter more blackish tones ( Bruchet 1970); a distinction that could not be supported by other lines of evidence. The holotype of H. kuehneri was lost, however, and a new lectotype (selected from the paratypes) has been established ( Beker et al. 2016; LY BR66-15); it is sequenced and is a molecular match to H. nigellum . We here follow Beker et al. (2016) in selecting the name H. nigellum over H. kuehneri for this species.