Pileus (Cap): 5 -- 10(15) cm, Convex or nearly flat with an incurved margin that slightly overhangs the gills. Buff yellow to warm buff orange, often slightly darker towards the center, dry, smooth, silky or finely floccose-fibrillose, sometimes floccose-sqaumulose toward the center, flesh firm, pale yellow. Staining orange-brownish or sometimes bluish-green where injured or on age.
Lamellae (Gills): Adnexed, thin, close, pale yellow, becoming rusty brown with age.
Stipe (Stem): 4 -- 8(9) cm, .5 -- 1.5 cm thick, equal to slightly enlarging below, solid, firm, colored like the cap, developing yellowish-rusty stains when handled, finely hairy, partial veil usually forms a fragile submembraneous ring or fibrillose annular zone near the apex. Staining orange-brownish or sometimes bluish-green where injured or in age.
Microscopic features: Spores rusty brown-orange in deposit, Spores 6 - 9 x 4 - 5(5.5) um minutely warty, elliptical, dextrinoid, surface finely roughened, no germ pore. Pleurocystidia present, cheilocystidia scarcely projecting beyond the basidia, variously shaped. Caulocystidia absent. Clamp connections present.
Season: June through November.
Habitat and Distribution: On dead hardwoods and probably conifers, widely distributed in eastern North America.
Growth Habit: Gymnopilus luteus is found growing solitary to gregariously or in small clusters
Bruising: Green or light blue bruising at the base on possibly on the pileus.
Other Notes: Often mistaken for Gymnopilus junonius. Gymnopilus luteus is a member of the Gymnopilus junonius (also known as "Gymnopilus spectabilis") species group. Like the other species in the group it grows on wood and has a medium sized or large cap, a partial veil that usually leaves a ring or ring zone on the stem, an orange to orange-brown spore print, and a bitter taste. Unlike the others, however, it is apparently limited to the hardwood forests of eastern North America, and features yellow colors as well as a slender stem.