Cap: 2 — 5(8) cm in diameter, convex becoming broadly convex to plane, silver-gray to brownish-gray, often with blue or greenish tint in age, smooth, with tiny scales near the center, darker at the margin, slightly translucent-striate when moist, unlined cap margin, flesh white with a grayish tinge, thin to moderate. Cap skin fibrous.
Gills: Crowded, broad, free, at first white, becoming pink-flesh colored; ventricose. Edges discoloring or bruising grayish.
Stipe: 3 — 5(10) long, 0.2 — 0.6 cm thick, more or less equal or slightly swollen at the base, flesh white with grayish-green to bluish-green tones, especially near the base. Ring absent. Firm, full or stuffed.
Taste: Unpleasant, indefinite or somewhat raphanoid (like radish).
Odor: Unpleasant, indefinite or somewhat raphanoid.
Spores: pink, smooth, 7 — 8.5 x 5 - 6 μm. Spore print pink-flesh colored to brown-pink.
Microscopic features: Pleurocystidiafusiform with slightly thickened walls 50 — 70 x 11 — 18 μm; with 3 — 5 horn-like projections.
It is always found growing on wood. Summer-fall, solitary or gregarious on dead wood of hardwoods, in damp forests on flood-plains.
Common name
The 'knackers crumpet' is a localised, common name referring to Pluteus salicinus. Its use is most prominent in the North of England.
Chemistry
The concentration of psilocybin and psilocin in the dried sample of P. salicinus has been reported in the range of 0.21-0.35 and 0.011-0.05%, respectively.[6][7]
^Christiansen, A. L.; Rasmussen, K. E.; Høiland, K. (August 1984). "Detection of psilocybin and psilocin in Norwegian species of Pluteus and Conocybe". Planta Medica. 50 (4): 341–343. doi:10.1055/s-2007-969726. PMID17340325.
^Ohenoja, E.; Jokiranta, J.; Mäkinen, T.; Kaikkonen, A.; Airaksinen, M. M. (Jul–Aug 1987). "The occurrence of psilocybin and psilocin in Finnish fungi". Journal of Natural Products. 50 (4): 741–744. doi:10.1021/np50052a030. PMID3430170.
Stamets, Paul (1996). Psilocybin Mushrooms of the World. Berkeley: Ten Speed Press. ISBN0-9610798-0-0.