Hebeloma (Fr.) P. Kumm.

Eberhardt, Ursula, Beker, Henry J., Borgen, Torbjorn, Knudsen, Henning, Schuetz, Nicole & Elborne, Steen A., 2021, A survey of Hebeloma (Hymenogastraceae) in Greenland, MycoKeys 79, pp. 17-118 : 17

Hebeloma (Fr.) P. Kumm.

General description.

Cap 0.9-21 cm, convex or more rarely campanulate or applanate, rarely depressed at center, dry, in wet weather viscid in some species, or tacky, smooth or rarely scaly, margin even or undulate, smooth, rarely hygrophanous, rarely striate, several shades of brown, from whitish to pale beige to dark brown, occasionally orange-brown, rarely reddish brown, along margin with or without remnants of universal veil, floccose or velutinate. Lamellae emarginate to adnate, thin, unicolored, at first pale, at maturity browner, in some groups with hyaline or brown droplets along margin. Stem 2.0-14.0 × 0.1-2.0 cm, cylindrical or bulbous at base, occasionally rooting, at first white, whitish or cream, becoming pale ochraceous to brown or even black, white tomentose, floccose or pruinose, rarely velutinate, some groups with partial veil, rarely with a membranous ring. Flesh color resembling the color of the stem, often discoloring brownish from stem base when bruised or old. Smell often radish-like, in one section sweetish, in some species insignificant. Taste mild to bitter, rarely significant. Spore deposit umber to dark cinnamon or dark brick red.

Spores most often amygdaloid, also ellipsoid or limoniform, rarely fusoid or navicular, in some species distinctly papillate, from pale yellow to dark brown, almost smooth to distinctly verrucose and ornamented with separate or coherent irregular warts, in some groups with ± loosening perispore, in Melzers solution from indextrinoid to distinctly and strongly dextrinoid. Cheilocystidia present in all species, variable but distinctive, cylindrical, lageniform, slenderly clavate, spheropedunculate, ventricose or balloon-shaped or variations thereof, rarely forked, in some species partially thick-walled, straight, sinuate or geniculate, hyaline or pale brown. Pleurocystidia rarely present, when present usually similar to cheilocystidia. Caulocystidia present in all species, similar to cheilocystidia, often fasciculate. Basidia cylindrical to slenderly clavate, 4-spored, rarely also 2-spored, in one arctic species only 2-spored. Pileipellis an ixocutis, a thin layer of narrow, hyaline hyphae, smooth or encrusted, 30-250 µm thick.

Comments.

Hebeloma is a genus of ectomycorrhizal fungi. The symbionts belong to a wide variety of families of dicotyledons. In Greenland, according to the observations of T.B., S.A.E. and H.K.K. symbionts appear to belong to the families: Salicaceae , Betulaceae , Polygonaceae and Rosaceae . The total list consists of only 11 species: Salix glauca , S. herbacea , S. arctica Pall., S. arctophila , Betula pubescens var. pumila , B. nana. , B. glandulosa , Alnus alnobetula subsp. crispa , Bistorta vivipara , Dryas octopetala and D. integrifolia .

Bistorta vivipara (L.) Delarbre (≡ Polygonum viviparum L., Polygonaceae ) has often been observed close to species of Hebeloma and Brevik et al. (2010) isolated sequences of Hebeloma spp. from its roots in Spitsbergen, which is normally considered as a strong indication that this plant associates with the respective fungus. In a few cases, T.B. found rhizoids from Hebeloma attached to the roots of Bistorta , but found it difficult to rate the importance of these observations, since there have often been other possible hosts observed nearby. For Alnus , there is no evidence that it is a host; for the few records from Alnus -shrubs, it is not possible to rule out nearby willows or birches. The remaining perennial shrubs in Greenland, Sorbus groenlandica (C.K. Schneid.) Á. Löve & D. Löve and Juniperus communis L. do not form ectomycorrhiza. This is also the case for members of the heather family ( Ericaceae ) that occur in Greenland, with the rare exception of Arctostaphylos alpina .