Psilocybe yungensis

A species of Psilocybe.

The P. yungensis mushroom features caps that, upon reaching maturity, exhibit a shape ranging from conical to bell-shaped, with a maximum diameter of 2.5 cm (1.0 in). The cap's surface is smooth and retains a sticky feel; in damp conditions, subtle radial striations (grooves) become visible, extending nearly to the edge. The coloration of fresh caps varies, appearing as dark reddish-brown, rusty brown, or orangish-brown. Furthermore, the cap is hygrophanous, meaning its color shifts with hydration levels; a dry cap will fade to a dull yellowish-brown or a dingy straw hue. A prominent central bump (umbo) is often present on the cap.

The gills attach to the stem in a manner ranging from broadly fused (adnate) to narrowly attached (adnexed). These slender gills are closely spaced, often crowded, and initially appear dull gray, later transitioning to a purplish-brown as spores mature. The stem measures 3 to 5 cm (1.2 to 2.0 in) in length and 1.5 to 2.5 mm (0.06 to 0.10 in) in thickness, generally maintaining a consistent width throughout or being slightly wider at the base. This hollow, fragile stem is pale brown towards the top and reddish-brown closer to the bottom. It is densely covered with flattened, whitish fibrils which eventually detach, leaving a smooth surface in mature specimens.

The mushroom possesses a ephemeral, cobweb-like partial veil (cortina) similar to those found in Cortinarius species. This veil is not long-lasting and may occasionally leave behind scattered tissue fragments on the cap margin and the upper stem. No persistent ring forms on the stem once the veil disappears. All parts of the mushroom will bruise blue when damaged, and these blue stains will darken to black as the mushroom dries.

Under 100x magnification, the cap cuticle, cap tissue, and gill tissue exhibit specific characteristics. The spore print is dark purplish-brown. Spores vary in shape from roughly rhomboid to elliptical, typically measuring 5–6 by 4–6 µm. They possess thick walls and a prominent germ pore. The basidia (spore-producing cells) are club-shaped to swollen, transparent (hyaline), typically bear four spores (though two- or three-spored forms are rare), and measure 13–19 by 4.4–6.6 µm.

Pleurocystidia (cystidia on the gill face) are swollen near the base (ventricose) and often terminate in a short, sharp point (mucronate), measuring 14–25 by 4.4–10.5 µm. Cheilocystidia (cystidia on the gill edge) display variable shapes and measure 14–40 by 4.4–7.7 µm. Pleurocystidia are relatively scarce, while cheilocystidia are abundant. Clamp connections are identifiable in the hyphae. Applying a drop of potassium hydroxide solution causes both the cap and stem to change color from brown to blackish.