Gymnopilus

The genus Gymnopilus — commonly called “rustgills” — contains roughly two hundred species of wood-decay mushrooms found worldwide. Most species are saprotrophs that grow on decaying conifer or hardwood, often producing dense clusters of fruiting bodies on logs and stumps.

The genus takes its common name from the rusty orange to bright yellow-brown coloration of its caps and gills. The spore print is itself rusty orange — a feature that distinguishes Gymnopilus from the dark purple-brown spores of Psilocybe and the black spores of Panaeolus.

Several Gymnopilus species contain psilocybin, psilocin, and the related compound hispidine. The most studied is G. junonius (also known historically as G. spectabilis), a large, conspicuous species found across temperate forests of both hemispheres. G. luteofolius and G. luteoviridis are also documented producers.

Identification can be difficult because not all Gymnopilus species produce indole alkaloids, and several non-psychoactive species in the genus closely resemble the active ones. Field identification carries the additional complication that some Gymnopilus species are intensely bitter, while a few others — including some psilocybin-producing species — taste differently.