Pileus 2-4 cm broad, obtusely conic or obtusely umbonate when young, expanding to obtusely campanulate and finally with a spreading or uplifted margin which may become wavy, usually retaining a slight obtuse umbo, smooth, viscid to glutinous when wet, soon dry, glabrous except for pallid, fibrillose remains of the veil along the margin, color brilliant pinkish orange ("flame-scarlet" to "bittersweet-orange"), fading somewhat in age and soon developing blackish discolorations. Context moderately thick, tapered evenly to the margin (about 4 mm in the disc), pliant and watery, "Mikado-orange" but soon paler yellowish orange; odor none, taste bitter.
Lamellae sharply and deeply adnexed, at times appearing to be almost free, close, 2-3 tiers of lamellulae, moderately broad (3-4 mm), "capucine-yellow" (orange-yellow) but discoloring somewhat where bruised, edges even.
Stipe 5-9 cm long, 4-7 mm thick, equal, terete, hollow, flexuous, apex "cream-color" within, in the base sordid orange buff, surface more or less fibrillose and pallid yellowish from the yellow veil, base tinged faintly like the pileus and soon sordid orange, brown where handled, glabrescent.
Spores 5-7 X 3.8-4.5 Âµ, smooth, germ pore minute and apex not truncate; shape in face view ovate to elliptic, in profile somewhat inequilateral to obscurely so; revived in KOH rusty brown, in Melzer's reagent paler and more cinnamon; wall about 0.3 Âµ thick.
Basidia 18-26 X 5-7 Âµ, 4-spored, narrowly clavate, yellowish in KOH and in Melzer's reagent. Pleurocystidia 35-60 X 8-14 Âµ, fusoid-ventricose to clavate-mucronate, base often 6-8 Âµ or more broad, wall thin and smooth, apex obtuse to subacute; content amorphous-refractive and in some organized into a solid refractive mass, in others more or less resembling coagulated material and somewhat granular in appearance, both types intergrading, the coagulated content bright yellow in KOH and orange to orange-red in Melzer's reagent. Cheilocystidia 40-75 x 4-8 x 3-4.4 Âµ ventricose at base and neck a long cylindric tube ending in an obtuse apex, walls at times with adhering debris and often yellowish in KOH. Caulocystidia none found except for a few clavate hyphal endcells.
Gill trama with a central area of greatly inflated hyphal cells (to 20 Âµ or more); subhymenial area of narrower (3-6) Âµ, non-gelatinous hyphae, yellow pigment in solution pervading the section. Pileus cutis a gelatinous pellicle of hyaline to yellow interwoven hyphae 2-5 p. diam.; hypodermial region more ochraceous, cells compactly arranged and 8-12 (20) Âµ broad. Context hyphae interwoven, of very broad cells, smooth, yellow pigment spreading throughout the mount. Clamp connections present. All hyphae inamyloid.
Habit, Habitat, and Distribution: On logs, stumps, and rotting wood of conifers, California, Michigan, Tennessee, Idaho, Oregon and Washington. August to October.
Observations: The bright colors of the pileus, bitter taste, and the development of black discolorations are distinctive features of this species. It appears related to P. piceina, which is bright yellow with a darker, reddish disc, with greenish yellow context, smaller cheilocystidia, narrow tramal hyphae of the lamellae, and in having a distinct hypodermium. The pileus trama and gill trama are brown or yellowish brown in KOH but slowly fade out to nearly hyaline. When sections dipped in 95% alcohol and then in water are mounted in 2% KOH, a greenish yellow pigment diffuses into the mounting fluid. The curious cheilocystidia are a unique character in the genus.
Material Examined: CALIFORNIA: Smith 8812: IDAHO: Smith 70251; MICHIGAN: Smitll 33-750, 25881, 37409, 38522, 38655; MONTANA: Kauffman 7-8-28; NORTH CAROLINA: Hesler 19298; OREGON: Gruber 687; KAUFFMAN: 10-14-22, 10-15-22; Smith 18747, 20187, 20231, 20243, 28419, 28249; WASHINGTON: Kauffman 10-17-15a, 10-17-15b, 10-14-25, 10-25-25; Smith 3094, 16246, 16446, 16704, 16749, 16856, 17102, 17844, 30108, 31493, 31780. CANADA: ONTARIO: Smith 4533. FRANCE: Josserand 30-8-37. SWEDEN: Kauffman 10-1808. SWITZERLAND: Favre.