Summary:
Section Hebeloma. The important combination of characters for the North American material of the type variety, according to Smith(7), is a dark brown cap when moist, a stem darkening at base with the change progressing upward, a white veil, either the taste or the odor radish-like, the taste usually becoming bitterish, spores 8-10(11) x 5-6 microns, and not truly inequilateral but +/- bean-shaped in side view, many cheilocystidia ventricose at or near the base, the wall of the neck wavy to irregular, and the apex typically subacute to obtuse (not significantly enlarged). |Beker(1) emphasized (for Europe) the typically buff to grayish brown two-colored cap with a more intensely brown centre, the presence of a cortina, elliptic spores that are fairly small, pale, weakly ornamented, and non-dextrinoid (or weakly dextrinoid), and lageniform or ventricose cheilocystidia. |Smith(7) describe also var. lateritium (from WA) with a brick red disc, a thick stem (0.7-1cm) not discoloring markedly, and a copious white veil, var. subobscurum (from ID) with a dull dry appearance to the fresh cap, gills that are pinkish gray at first, and pallid veil, and 9 more varieties from CO, some of which could actually be species. |The description from Smith(7) for the type variety is followed here by the Beker(1) description for European material, and then by a composite description from field guides giving some idea of the variety of characters ascribed to what is commonly known as Hebeloma mesophaeum. |Hebeloma strophosum is considered by Beker(1) to be Hebeloma mesophaeum - it was described from Sweden, Smaland with no designated type: "Based on the protologue where this species is described from Sweden with a veil, in pine forests, it seems highly likely that this is = Hebeloma mesophaeum (Pers.) Quel." |H. mesophaeum is closely related to Hebeloma excedens, and the clade of species represented by Hebeloma alpinicola, Hebeloma nigromaculatum, and Hebeloma perigoense. (See H. alpinicola for the last three.) Unpublished research indicates that Hebeloma dunense and Hebeloma hygrophilum, also in Hebeloma Section Hebeloma, are also present in the Pacific Northwest (H. Beker, pers. comm.) and they were identified for Colorado too by Cripps(7). See SIMILAR section for differentiating features of H. dunense and H. hygrophilum from H. mesophaeum.

Gills:
narrowly adnate to adnexed or emarginate, close, broad, 3-4 tiers of subgills; at first whitish, finally "cinnamon-buff" to "sayal brown"; "edges white-floccose but not beaded", (Smith), "adnate to emarginate, sometimes with a decurrent tooth, rarely decurrent" (italicized), maximum breadth 0.2-0.65cm, 32-48 gills reaching stem, droplets occasionally visible with at 10x lens or rarely visible with the naked eye, edge usually white-fimbriate, (Beker), adnate to adnexed or notched, close, broad, intermediates present; whitish becoming gray-brown; edges usually whitish, serrate

Stem:
3-7cm x 0.3-0.8cm, equal or nearly so, not rooting, no mycelial cords; dingy brownish, darker in lower part especially when old, pallid near top; mealy near top, fibrillose-striate below, (Smith), 1.4-8.0(9.0)cm x (0.2)0.23-0.6(0.8)cm at mid-stem, (0.2)0.24-0.6(0.8)cm wide at base, base usually cylindric, rarely tapering or clavate, not rooting and no mycelial cords, stem interior "stuffed, later hollow, occasionally with superior wick" (italicized), stem surface "fibrillose, usually pruinose to floccose at apex" (italicized), (Beker), 3-9cm x 0.3-1cm, usually longer than width of cap, more or less equal; whitish to dingy brownish, slowly becoming dark brown from base up; fibrillose, top often farinaceous [mealy]

Veil:
"white to pallid, fibrillose, typically leaving remnants" on or near cap margin and/or on the stem, an annular zone often present, (Smith), cortina present, often cap has universal veil remnants, (Beker), webby pale yellow becoming brown from spores, leaving fibrillose superior ring zone

Odor:
of radish to not distinctive (Smith), usually raphanoid, rarely no odor, (Beker), typically radish-like, but can be mild or pungent or unpleasant

Taste:
of radish to not distinctive, usually becoming bitterish, (Smith), "mild to bitter, sometimes raphanoid", (italicized), (Beker) typically radish-like, but can be mild or bitter

Microscopic spores:
spores 8-10.5(11) x 5-6 microns, in face view elliptic to broadly ovate, in side view obscurely inequilateral, minutely marbled under high-dry lens, not dextrinoid, wall about 0.3 microns thick, pale ochraceous in KOH; basidia 4-spored, 24-34(40) x 7-9 microns; pleurocystidia none, cheilocystidia 30-54(70) x 5-12 x 3-5 microns, subcylindric to elongate fusoid-ventricose, colorless, "wall in neck often flexuous, often with a crook (knee-joint-like) near the base"; gill trama typical for the genus (lacking red tints in Melzer''s), cap cuticle a well-developed ixocutis to an ixolattice, hyphae with clamp connections, the walls refractive and the hyphae 1.5-4 microns in diameter; hypodermium cellular, the walls dark brown in KOH; tramal hyphae of the cap lacking a red reaction in Melzer''s reagent, (Smith), spores (6.4)7-12(15.1) x (4.1)4.2-7(7.5) microns, elliptic, occasionally oval, under microscope "yellow through yellow brown to brown" (italicized), variable guttulation, not papillate; basidia 4-spored (rarely 2-spored), (22.8)23.6-30.9(31.7) x (5.8)6.5-8.6(9.2) microns; cheilocystidia (21)28-80(86) x (2.3)3.5-7.2(9.4) microns at apex, (2.7)3.4-7.9(8.5) microns wide at middle, (3.7)6.4-13.6(14.4) microns wide at base, "lageniform, ventricose, occasionally cylindrical, rarely clavate" (italicized), occasionally "apical thickening, basal thickening, bifurcate, geniculate, septate (sometimes clamped)", pleurocystidia none usually but occasionally a few sparse pleurocystidia present; caulocystidia similar to cheilocystidia but less ventricose up to 130 microns long, (Beker), spores 8-11 x 4-7 microns, elliptic, slightly rough; pleurocystidia absent and cheilocystidia present

Spore deposit:
"Dresden brown" fresh, near "sayal brown" as air-dried, (Smith), "Isabella to brownish olive to umber" (italicized), (Beker), rusty to mud-brown, yellow or olive-brown

Notes:
H. mesophaeum var. mesophaeum is widely distributed throughout the western United States, and according to Smith(15) probably occurs throughout temperate North America. The varieties above were collected from WA, ID, and CO. In North America most collections that look like H. mesophaeum are a very closely related taxon called H. excedens, (Henry Beker, pers. comm.). There are collections of H. mesophaeum from BC at Pacific Forestry Centre and the University of British Columbia, and there are collections of H. mesophaeum from WA and Alaska at Oregon State University. The University of Washington has collections labeled as this species from BC, WA, ID, Alaska, ON, and Michigan. Unpublished research indicates that Hebeloma mesophaeum occurs in BC, WA, ID, and more widely in North America, (Henry Beker, pers. comm.).

EDIBILITY

poisonous, causing gastrointestinal upset