Libertycapz Psilocybe semilanceata, commonly known as the liberty cap, is a psychedelic (or "magic") mushroom that contains the psychoactive compounds psilocybin and baeocystin. Of the world's psilocybin mushrooms, it is the most common in nature, and one of the most potent. The mushrooms have a distinctive conical to bell-shaped cap, up to 2.5 cm (1.0 in) in diameter, with a small nipple-like protrusion on the top. They are yellow to brown in color, covered with radial grooves when moist, and fade to a lighter color as they mature. Their stems tend to be slender and long, and the same color or slightly lighter than the cap. The gill attachment to the stem is adnexed (narrowly attached), and they are initially cream-colored before tinting purple as the spores mature. The spores are dark purplish-brown in mass, ellipsoid in shape, and measure 10.5–15 by 6.5–8.5 micrometers.

The mushroom grows in fields, grassy meadows, and similar habitats, particularly in wet, north-facing fields (south-facing for southern hemisphere) that are well-fertilized by sheep and cattle feces. But unlike P. cubensis and P. coprophila, the fungus does not grow directly on dung; rather, it is a saprobic species that feeds off decaying grass roots. It is widely distributed in the cool temperate and subarctic regions of the Northern Hemisphere, particularly in Europe. However, it has also been reported occasionally from warmer locations such as India, South America, and Australasia. The earliest reliable history of P. semilanceata intoxication dates back to 1799 in London, and in the 1960s the mushroom was the first European species confirmed to contain psilocybin. Further investigations into the chemical makeup of the fungus revealed the presence of the substances phenylethylamine and the psychotropic baeocystin.