Hebeloma aurantioumbrinum Beker, Vesterh. & U. Eberh., Persoonia 35: 116 (2015)

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 : 14-17

2. Hebeloma aurantioumbrinum Beker, Vesterh. & U. Eberh., Persoonia 35: 116 (2015) Figures 4C, 8, 23 (2)

Etymology.

From aurantius, orange and umbrinus, umber.

Description.

Cortina absent. Pileus small, 10-20 mm in diameter, convex, slightly conic-convex, appearing smooth, greasy, not hygrophanous, cream, then buff, pinkish buff, orange brown, can be lighter towards margin but not clearly two-toned, somewhat hoary; margin weakly involute, possibly crenate with a white rim. Lamellae deeply indented, deeply sinuate-arcuate, rather distant, L = 25-40 plus lamellulae, cream, then buff, pinkish buff, milk coffee; edges fimbriate, white but graying, drops visible. Stipe 15-28 × 2-3 mm, equal, bit curved, dingy whitish cream but darkening at base to watery brown (in CLC3093), floccose/pruinose for top third and smooth-fibrous below. Context dingy whitish. Odor faint or raphanoid. Exsiccate: pileus buff, lamellae brown; stipe very thin, whitish.

Basidiospores yellowish brown, slightly amygdaliform, with almost obtuse ends, with tiny apiculus, with slight ornamentation (O2), no loosening perispore (P0, P1), slightly dextrinoid (D1, D2), 10 –13(– 14) × 6-7.5 µm, on average 11.5 × 6.7 µm, Q = 1.72. Basidia 30-35 × 8-10 µm, clavate, two- and four-spored. Cheilocystidia long with swollen apex, clavate-stiptate, occasionally clavate-lageniform, 40-70 × 6-9 µm at apex, 3-5.5 µm in middle, and 3-6.5 µm in base. Pleurocystidia absent. Epicutis thickness 70-100 µm, with some encrusted hyphae.

Rocky Mountain ecology.

In the alpine with willows Salix glauca , Salix planifolia , and S. arctica , reported from Colorado, Montana and Wyoming.

Rocky Mountain specimens examined.

U.S.A. COLORADO: San Juan/Hinsdale County, San Juan Mountains, Stony Pass, with Salix arctica , 28 July 2002, CLC1822 (MONT), C. Cripps. WYOMING: Park County, Beartooth Plateau. Frozen Lakes with S. planifolia , 14 Aug 2014, CLC3093 (MONT), C. Cripps; WY/MT stateline with S. planifolia , 14 July 2001, CLC1565 (MONT), C. Cripps. Wyoming Creek 6 Aug 2008 with S. arctica and S. glauca , HJB12445, C. Cripps & H.J. Beker; HJB12446, C. Cripps; HJB12447, C. Cripps; HJB12448, H.J. Beker; HJB12450, HJB12452, HJB12453, H.J. Beker; HJB12451 with S. planifolia , H. Knudsen; HJB12454, E. Horak. Upper Wyoming Creek, with Salix arctica , 8 Aug 2008, HJB12456, J. Antibus. Hell-Roaring Plateau, with Salix sp., 14 Aug 2007, ZT12730 (ETH), ZT12731 (ETH), E. Horak.

Discussion.

Beker and co-workers ( Beker et al. 2016; Eberhardt et al. 2015a) showed that H. aurantioumbrinum cannot be distinguished from the non-arctic-alpine H. helodes J. Favre based on ITS sequencing, but it can be separated from all other members of H. sect. Denudata . An ITS tree is given in Eberhardt et al. (2015a). The RM dataset includes more collections of H. aurantioumbrinum (15) than the FE dataset (7). Therefore, it is not surprising that the molecular diversity of the RM sequences is higher than that of the FE dataset (Fig. 4C). There are 0-6 [0] bp differences among the FE sequences of H. aurantioumbrinum , 0-9 [0-3] bp differences among the sequences of RM H. aurantioumbrinum and 2-11 [0-3] bp differences between H. aurantioumbrinum and H. helodes . Morphologically, H. aurantioumbrinum and H. helodes are quite different and can be easily separated, for example H. helodes always has a distinct thickening of the cheilocystidium wall at the apex, a feature that is absent in H. aurantioumbrinum . Further, they occur in very different habitats; H. helodes has never, to our knowledge, been confirmed in arctic-alpine habitats.

Hebeloma aurantioumbrinum may have been confused with H. pusillum J.E. Lange, although H. pusillum has much more slender basidiomes that are distinctly two-toned. Hebeloma aurantioumbrinum is squatter and rarely two-toned. Additionally, we are not aware of any confirmed records of H. pusillum in arctic-alpine habitats. Both these species, without any veil (beyond the primordial stage) and with clavate-stiptate cheilocystidia, belong to the Crustuliniformia subsection of section Denudata . This subsection contains many small species that are arctic-alpine specialists that occur with Salix , and these species have only recently been split out and described ( Eberhardt et al. 2015a). Collections of H. aurantioumbrinum have been confirmed from a number of arctic and alpine habitats, including Greenland, Iceland, Scandinavia, and Svalbard ( Beker et al. 2016). In the Rockies, this species can be recognized by its alpine habitat, association with willows (primarily S. planifolia ), small size, lack of veil, and pinkish buff to orange brown uniformly colored pileus often with a white, crenate margin.