Psilocybe guilartensis is a psilocybin mushroom which has psilocybin and psilocin as main active compounds. It is common in Puerto Rico.

First reported in the literature in 1997, Gastón Guzmán placed P. guilartensis in Psilocybe section Brunneocystidiatae due to its blue staining reaction, small thick-walled subrhomboid spores, and pigmented cystidia.

Other mushrooms in the section Brunneocystidiatae include Psilocybe banderillensis, Psilocybe banderillensis var. paulensis, Psilocybe brunneocystidia, Psilocybe heimii, Psilocybe inconspicua, Psilocybe pleurocystidiosa, Psilocybe rzedowski, Psilocybe singeri, Psilocybe uxpanapensis, Psilocybe verae-crucis and Psilocybe weldenii.

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