Hebeloma excedens (Peck) Sacc., Syll. Fung. 5: 806 (1887)

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 : 32-35

12. Hebeloma excedens (Peck) Sacc., Syll. Fung. 5: 806 (1887) Figures 6B, 18, 23 (12)

Etymology.

For the pileus cuticle which can exceed the lamellae.

Description.

Cortina present. Pileus 10-25 mm in diameter, shallow convex, campanulate, then almost applanate, slight umbo or not, viscid or greasy, medium cocoa brown to orange caramel in center and pale brown on most of the pileus, with or without white tissue at margin, or with whitish rim; margin originally described as extending beyond the lamellae. Pileus thin-fleshed. Lamellae sinuate, subdecurrent, narrow, becoming broader and eroded, very pale, cream with pinkish buff tint, L = 32-48 plus lamellulae. Stipe 30-50 × 2-4 mm, equal, slightly curved, pale cream, silky, pruinose above ring zone, more dingy brown below but still pale, with a golden brown fibrils in zones, blackening towards base. Context whitish in pileus and stipe apex and yellowish brown in lower stipe down to blackish at base; stipe tough, rubbery. Odor: raphanoid or none. Exsiccate: small, pale buff overall, base of stipe dark in some.

Basidiospores yellow brown, elliptical, a few slightly ovoid, no big apiculus, not guttulate, looks almost smooth to very slightly rough even under high magnification (O1), not or only very slightly dextrinoid (D0,D1), and no perispore loosening (P0), 7-11 × 5-6.5 µm, on average 9.1 × 5.8 µm, Q = 1.55. 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, 30-60 µm long × 4-7 µm at apex, 4-6.5 µm in middle, and 6-10 µm wide at base, some septate. Epicutis thickness 65-200 µm, with some encrusted hyphae.

Rocky Mountain ecology.

In alpine with shrub willow Salix glauca , Colorado.

Rocky Mountain specimens examined.

U.S.A. COLORADO: San Juan County, San Juan Mountains. U.S. Basin, 3658 m, with Salix glauca , 8 Aug 2001, CLC1685 (MONT), C. Cripps. Sawatch Range, Independence Pass, 14 Aug 1999 with Salix sp., ZT7475 (ETH), E. Horak; 12 Aug 1999 with Salix sp., ZT8136 (ETH), E. Horak; 14 Aug 2001 with Salix glauca and S. planifolia , ZT9830 (ETH), E. Horak; 3760 m, with Salix glauca , 13 Aug 2001, CLC1732 (MONT), C. Cripps. Front Range, Loveland Pass, 7 Aug 1999 with Salix sp., ZT8074 (ETH), E. Horak.

Other specimens examined.

NEW YORK: Saratoga at approx. 100 m, with Pinus sp. on sandy soil in woodland, Oct 1870, NYS-F-001123, C.H. Peck (holotype).

Discussion.

Hebeloma excedens was not treated by Beker et al. (2016). The type of H. excedens fits in with the majority of the RM H. excedens collections, but the species cannot be clearly separated from H. mesophaeum (Fig. 6B). Looking at absolute differ ences, the intraspecific variation of the H. excedens sample (RM + type = 7 sequences) is 0-8 [0-1] bp, whereas the variation in the sample between H. excedens and H. mesophaeum is 2-11 [0-4] bp. In terms of absolute differences, the type of H. excedens is 5-8 [0-1] bp different from other collections referred to this species, but as Fig. 6B shows it is not strongly differentiated from other members of H. excedens , if ambiguous positions are treated as missing data as in networks or equated to their constituting bases as in the ML tree. In terms of absolute differences, the type of H. excedens is 5-11 [0-3] bp away from the H. mesophaeum sequences of the sample. Thus, within the limited support ITS data can give in this case, we do consider the species identification of the RM H. excedens collections as molecularly supported. Until the question of the distinctness and delimitation of this species can be clarified, we prefer to treat it as an independent taxon.

Hebeloma pubescens Beker & U. Eberh. is another species from the H. mesophaeum complex that might occur in the sampled habitats of the Rocky Mountains and is close to H. excedens in Fig. 6B. Based on a small sample (3 sequences available for H. pubescens ; 7 sequences for H. excedens ), the species vary 5-10 [1-3] bp in their ITS region.

Hebeloma excedens was first described by North American mycologist C.H. Peck; the species, with its lageniform to ventricose cheilocystidia and small elliptical, almost smooth, indextrinoid spores belongs to H. sect. Hebeloma . It is closely allied with Hebeloma mesophaeum , with which we believe it has often been confused. Separating these two taxa morphologically is rather difficult, but it does appear that the pileus of H. excedens may be more evenly colored, less yellow brown, less brown in the center, and it was originally described as having a cuticle that extended beyond the lamellae. The stipe surface appears to have fibrils arranged in zones, in contrast to that of H. mesophaeum . However, further work is required before we can have confidence that these characters are consistently different.

We have examined a number of collections from North America that are morphologically and molecularly consistent with this taxon. Based on these studies it would appear that Hebeloma excedens is widespread across North America and occurs in a wide variety of habitats.