Psilocybe yungensis

A species of Psilocybe

The P. yungensis fruit bodies have caps that are conical to bell-shaped in maturity, and reach a diameter of up to 2.5 cm (1.0 in). The cap surface is smooth and sticky, and, in moist specimens, has faint radial striations (grooves) that extend almost to the margin. The color of fresh caps ranges from dark reddish-brown to rusty brown to orangish-brown. Additionally, the cap is hygrophanous, meaning it will change color depending on its state of hydration; a dry cap fades to become dull yellowish-brown or the color of "dingy straw". The cap frequently has a prominent umbo. The gill attachment ranges from adnate (broadly attached to the stem) to adnexed (narrowly attached). The spacing of the narrow gills is close to crowded, and the gill color is initially dull gray before maturing spores cause the color to change to purplish-brown. The stem is 3 to 5 cm (1.2 to 2.0 in) long and 1.5 to 2.5 mm (0.06 to 0.10 in) thick, and more or less equal in width throughout its length or slightly larger near the base. The hollow, brittle, stem is pale brown on the upper part, and reddish-brown near the bottom. The stem is densely covered with whitish fibrils that are pressed flat against the surface; the fibrils slough off in maturity to leave a smooth surface. The mushroom has a cortinate partial veil (resembling the webby cortina produced by species of Cortinarius) but it does not last for long; it occasionally leaves behind sparse remnants of tissue hanging on the cap margin and the upper part of the stem. No ring remains on the stem after the veil disappears. All parts of the mushroom will stain blue when injured; these stains will blacken as the mushroom dries. Cap cuticle, cap tissue, and gill tissue at 100x magnification The spore print is dark purplish-brown. Spores range in shape from roughly rhomboid to roughly elliptical, and typically have dimensions of 5–6 by 4–6 μm. They are thick-walled and have a large germ pore. The basidia (spore-bearing cells) are club-shaped to swollen, hyaline, usually four-spored (although rarely two- or three-spored forms are present), and measure 13–19 by 4.4–6.6 μm. The pleurocystidia (cystidia on the gill face) are ventricose (swollen) near the base and often mucronate (ending abruptly in a short sharp point) at the apex, and measure 14–25 by 4.4–10.5 μm. The cheilocystidia (cystidia on the gill edge) are variable in shape, and measure 14–40 by 4.4–7.7 μm. Pleurocystidia are relatively sparse, while cheilocystidia are abundant. Clamp connections are present in the hyphae. The application of a drop of potassium hydroxide solution turns both the cap and the stem from brown to blackish.