Cap 2-4.5 cm broad, convex, becoming nearly plane with a low umbo; margin striate, often wavy, sometimes upturned in age; surface smooth, sticky when moist, hygrophanous, brown, fading to yellow-brown or buff; flesh thin, brittle in age, bruising blue.
Gills adnate to seceding, close when young, subdistant in age, pale cinnamon brown, becoming dark grey-brown, edges lighter than the faces, mottled from spores at maturity.
Stipe 3-6 cm tall, 3-6 mm thick, equal to sometimes enlarged at the base, the latter with conspicuous thickened mycelium (rhizomorphs); surface white, smooth to silky, bruising blue; veil fibrillose, forming a superior, evanescent hairy, annular zone.
Spores 9-12 x 6-8 µm, elliptical, smooth, with an apical pore; spore print purple-brown to purple-grey.
Scattered to gregarious on woody debris, leaf litter, and wood chips; fruiting from late summer in watered areas to mid-winter.
Psilocybe cyanescens is recognized by a chestnut-brown, striate, wavy-margined cap that soon fades to yellow brown or buff, and blue-staining fruiting body. Because of its hallucinogenic properties, it is sometimes the subject of experimentation, a potentially dangerous practice because of toxic look-alikes in Galerina, Conocybe and Inocybe.