Pileus (Cap): The cap is convex to bell-shaped, sometimes developing a broad umbo before expanding and flattening in age; it reaches a diameter of 1.5%u20132 cm (0.6%u20130.8 in). In maturity, the cap eventually forms a central depression, and, in some old specimens, opens into the hollow stem. The cap surface is slimy to the touch, and has translucent striations along the margin when moist. The cap is strongly hygrophanous, meaning that it will change color depending on its level of hydration. The color ranges from yellowish-brown to golden yellow in young button forms to brownish-gray in age, with greenish-gray tints on the margin. The color later changes to whitish from the center to the margin, finally remaining completely white; dried specimens are straw colored to pale brownish. In contrast to most psilocybin mushrooms, the cap of P. aztecorum does not have a strong bluing reaction upon injury%u2014only the margin stains slightly green-blue.
Lamellae (Gills): The gills are adnate (broadly attached to the stem slightly above the bottom of the gill) or adnexed (reaching the stem, but not attached to it), and are light violet gray to dark violet brown. They are either uniform in color, or have whitish edges.
Stipe (Stem): The hollow stem is 5.5 to 7.5 cm (2.2 to 3.0 in) by 3 to 4 mm (0.12 to 0.16 in) thick, equal in width throughout or thicker at the top, cylindric or sometimes flattened, and either straight or with turns and windings. Its surface is smooth, silky-fibrillose, whitish to greyish, and stains blue-green irregularly when touched or in age. The base of the stem is densely covered with well-developed white rhizomorphs. Young mushrooms have a white cobweb-like partial veil that does not last long before it disappears, although it sometimes remains as a non-permanent ring on the upper part of the stem. The flesh is whitish to yellowish or reddish-yellow in the cap, or reddish-brown in the stem, and shows little or no bluing reaction to injury. Like most of the bluing Psilocybe mushrooms, the odor and taste of P. aztecorum is slightly farinaceous (similar to freshly ground flour) in fresh specimens; dried specimens have a more intense odor. A drop of dilute potassium hydroxide (KOH) stains the cap, stem, and flesh reddish-brown; sometimes, the stem does not stain or stains slightly yellowish red. The spore print is blackish-violet.
Microscopic features: The spores are elongated-ellipsoid in face view, roughly terete (more or less cylindrical but usually tapering at both ends), slightly inequilateral or asymmetrical in side view%u2014the so-called "mango" form. They typically have dimensions of 12%u201314 by 6.6%u20137.7 by 6%u20137.5 %u03BCm, although some spores have irregular shapes and are strongly elongated, up to 23 %u03BCm. Spores are thick-walled (generally between 1%u20131.5 %u03BCm), dark yellowish-brown, and have a broad germ pore. The variety bonetii has smaller spores measuring 10%u201313 by 6%u20137.5 by 6%u20137 %u03BCm. The basidia (spore-bearing cells) measure 24%u201333 by 6.6%u20138.8 %u03BCm, and may be attached to anywhere from one to four spores, although four-spored basidia are most common. They are hyaline to sometimes somewhat yellowish, club-shaped or roughly cylindrical, and some have a slight constriction around the middle. The cheilocystidia (cystidia on the edge of a gill) are abundant, forming a sterile band on the gill edge. They are hyaline, fusoid-ampullaceous (with a shape ranging from a spindle to a swollen bottle), with dimensions of 20%u201345 by 5%u20138.2 %u03BCm, and have a filamentous neck measuring 6%u201311 by 1.6%u20132.5 %u03BCm. The pleurocystidia (cystidia on the gill face) are scattered, similar to the cheilocystidia in form and size, hyaline, and some have bifurcated or branched necks.
Season: P. aztecorum fruits from August to October.
Habitat and Distribution: A lignicolous species, Psilocybe aztecorum lives in and decays dead wood, leaves, sticks, or other similar organic debris. Usual substrates include wood debris buried in soil, twigs or very rotten logs, and, rarely, pine cones. The mushroom is found in woodlands (a low-density forest or wooded area that allows sunlight to penetrate to the forest floor) containing Hartweg's Pine (Pinus hartwegii) in addition to grasses such as Festuca tolucensis and Muhlenbergia quadridentata, and the herbaceous plant Alchemilla procumbens, at elevations of 3,200%u20134,000 m (10,500%u201313,000 ft). Heim found the type specimens at an altitude of 3,500 m (11,500 ft) in an alpine pine forest.
Growth Habit: Mushrooms typically fruit in groups of 5 to 20, sometimes in bundles.
Bruising: Bruising blue when injured.
Dosage: A farily potent species. 2-4 grams dried.
Other Notes: Psilocybe aztecorum contains the psychoactive compound psilocybin. In 1958, Swiss chemist Albert Hofmann reported a relatively low concentration of 0.02% psilocybin, but this analysis was performed on two-year-old specimens. Jonathan Ott and Guzman indicated the presence of psilocybin in the variety bonartii. In terms of psychoactive potency, Paul Stamets rates P. aztecorum as "moderately to highly active". The statue of the Aztec "god of flowers", Xochipilli, a 16th-century stone effigy unearthed on the side of the volcano Popocatepetl, depicts a single figure seated cross-legged upon a temple-like base; his body is covered in carvings of sacred and psychoactive organisms. Circular patterns on his kneecaps, right forearm, and headdress have been interpreted by R. Gordon Wasson as stylized fruit bodies of Psilocybe aztecorum. Wasson says that the convex shape and incurved margins depicted in these images show the mushroom caps just before maturity. P. aztecorum is, in addition to P. caerulescens, one of two mushrooms thought to be the species described by 16th-century Spanish chronicler Bernardino de Sahagun as the teonanacatl ("flesh of the gods"). These mushrooms, considered holy sacraments by the Aztecs, were consumed during spiritual and divinatory rituals to induce hallucinatory visions.