|gills on hymenium|
|cap is convex|
|hymenium is adnexed or adnate|
|stipe has a ring|
|spore print is yellow-orange|
|ecology is saprotrophic|
|edibility: inedible or psychoactive|
Gymnopilus luteus also called the "Yellow Gymnopilus" is a widely distributed mushroom of the Eastern United States, it contains the hallucinogens psilocybin and psilocin. Often mistaken for Gymnopilus speciosissimus and Gymnopilus subspectabilis.
- Pileus: 3 — 20(25) cm, Convex-hemispherical at first, expanding to broadly convex, with an irregularly infolded and not 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. 
- Gills: Adnexed, thin, close, pale yellow, becoming rusty brown with age.
- Spore Print: Rusty brown.
- Stipe: 4 — 10(15) cm, .5 — 3 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.
- Taste: Bitter.
- Odor: Gills have the strong odor of anise, which is one of the easiest ways to differentiate it from its close relatives.
- Microscopic features: Spores (6.2–)6.5–8.3(–9.4) µm × (4.3–)4.5–5.7(–6.1) µm (average = 7.4 ± 0.5 m × 5.1 ± 0.3 m) µm, minutely warty, elliptical, slightly dextrinoid, surface finely roughened with irregular warts and short ridges, no germ pore. Pleurocystidia absent or very rare, cheilocystidia mostly lageniform to lecythiform but occasionally without a swollen apex; length = 19.3–35.4(–36.7) µm, average = 27.3 ± 4.0 µm. Caulocystidia abundant above the annular zone, produced as terminal cells of long hair-like hyphae, narrowly ventricose–capitate to cylindric–capitate, often cylindrical to clavate and without significant apical swelling; (28.6–)30.9–66.9 µm. Clamp connections present.
- Bruising: Green or light blue bruising at the base on possibly on the pileus.
It is considered inedible due to the bitter taste and presence of the hallucinogenic drugs psilocybin and psilocin.
Habitat and formation
Gymnopilus luteus is found growing solitary to gregariously or in small clusters on dead hardwood trees, June–November, widely distributed in eastern United States and Canada.
- Thorn, R. Greg; Malloch, David W.; Saar, Irja; Lamoureux, Yves; Nagasawa, Eiji; Redhead, Scott A.; Margaritescu, Simona; Moncalvo, Jean-Marc (2020-04-24). "New species in the Gymnopilus junonius group (Basidiomycota: Agaricales)". Botany. Canadian Science Publishing: 293–315. doi:10.1139/cjb-2020-0006. ISSN 1916-2790.