Hebeloma mesophaeum (Pers.) Quel ., Mem . Soc. Emul . Montbeliard , ser . 2, 5: 128 (1872)

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 : 32

11. Hebeloma mesophaeum (Pers.) Quel., Mem. Soc. Emul. Montbeliard, ser. 2, 5: 128 (1872) Figures 6B, 17, 23 (11)

Etymology.

From Greek meso, in the middle, and phaeus, dark-colored. Persoon (1872) particularly mentioned the peculiar reddish brown pileus center "disco rufo-fusco peculiaris" which is characteristic of this taxon.

Description.

Cortina present. Pileus 10-20 mm in diameter, convex with low indistinct umbo, or conic-convex, smooth, shiny, greasy, yellowish brown in center, outwards lightening to pale ocher, at margin buff, two-toned, non-translucent; margin entire, turned in when young, covered with veil or not. Lamellae attached, adnate, L = 38-40, pale buff, pinkish buff, then pinkish brown; edges fimbriate. Stipe: 30-45 × 3 –5(– 8 at base), very gradually larger at base, white, pruinose at apex, and fibrillose and darker below to ocher yellow and then blackish at very base. Context pale, dark in base of stipe. Odor raphanoid. Exsiccate: pileus pale brown, stipe with yellow sheen and darker at base.

Basidiospores yellow brown, elliptical, a few slightly ovoid, no big apiculus, not guttulate, looks almost smooth even under high magnification (O1), not or only very slightly dextrinoid (D0, D1), and no perispore loosening (P0), 8 –10.5(– 11) × 5-6.5 µm, on average 9.7 × 5.8 µm, Q = 1.66. Basidia 20-30 × 6-9 µm, clavate, four-spored mostly. Pleurocystidia absent. Cheilocystidia cylindrical in the upper part and slightly swollen to more swollen at the base, rarely fully cylindrical, 30-55 µm long × 4-7 µm at apex, 4-7 µm in middle, and 6 –9.5(– 10.5) µm wide at base, with occasional thickening of the apical wall, some septate. Epicutis thickness 60-350 µm, with some encrusted hyphae.

Rocky Mountain ecology.

Known so far only from the Colorado alpine with Salix glauca.

Rocky Mountain specimens examined.

U.S.A. COLORADO: Sawatch Range, Independence Pass, 3760 m, with Salix glauca , 8 Aug 1998, CLC1245 (MONT), C. Cripps; Front Range, Loveland Pass, 7 Aug 1999 with Salix sp., ZT8082 (ETH), E. Horak.

Discussion.

Only two collections from the RM dataset turned out to be H. mesophaeum that differ in their ITS region by 7 [2] bp (Fig. 6B). The sequence variation among all H. mesophaeum sequences (12) of the sample is 1-11 [0-4] bp. Beker et al. (2016) did not manage to delimit H. mesophaeum based on several loci. They suspected that there might be several species hidden within the sample assigned to H. mesophaeum . It appears likely that H. excedens and H. alpinicola are among these ‘cryptic’ taxa. We made sure that the 10 selected sequences from the FE dataset belong to H. mesophaeum in the strict sense. Among the H. mesophaeum representatives of the RM dataset, there is one collection that is reminiscent of H. pubescens . However, because of its ambiguous morphology we decided to keep it in H. mesophaeum . The respective collection (CLC1245) differs by 2-4 [1-2] bp from the available H. pubescens data (3 sequences).

Previously Hebeloma bruchetii Bon was one of the most commonly reported species from arctic and alpine areas, but it has now been synonymized with and folded into H. mesophaeum ( Beker et al. 2016). Hebeloma mesophaeum has relatively small elliptical spores that are smooth to slightly rough and not dextrinoid. Hebeloma mesophaeum is a widespread species reported in almost all arctic and alpine habitats, as well as from subalpine, boreal, and lower elevation habitats with a wide variety of hosts ( Beker et al. 2016). Also, many varieties have been described in North America ( Smith et al. 1983) and in Europe ( Vesterholt 2005). Some of the European taxa have been synonymized by the authors ( Beker et al. 2016) and it remains to check the 12 North American varieties delineated by Smith et al. (1983).