Gymnopilus sapineus is a small and widely distributed mushroom which grows in dense clusters on dead conifer wood. It has a rusty orange spore print and a bitter taste and contains the hallucinogen psilocybin.
This mushroom is often mistaken for Gymnopilus luteocarneus which grows on conifers and has a smoother and darker cap. Another lookalike is Gymnopilus penetrans which grows in the same habitat and has minor microscopic differences. 
Cap: 2.5 to 6 cm across, is convex, and is golden-yellow to brownish orange, darker at the center with a dry scaly surface which is often fibrillose and may have squamules. The cap margin is inrolled at first and curves outward as it matures, becoming almost plane and sometimes developing fibrillose cracks in age. The flesh is yellow to orange.
Gills: and the gills are crowded, yellow at first, turning rusty orange as the spores mature, with adnate attachment.
Stipe: 2.5 - 7 cm long, .5 cm thick, equal or becoming thinner near the base. Light yellow, bruising rusty brown. Has an evanescent veil which often leaves fragments on the upper part of the stem or the margin of young caps.