From what source is psilocybin typically obtained?

Psilocybin is a naturally occurring psychedelic compound primarily found in certain species of mushrooms, often referred to as "magic mushrooms." These mushrooms belong to the genus Psilocybe, among others. The presence of psilocybin in these fungi has been well-documented in scientific literature, making them the primary source of this substance.

In contrast, the other options do not provide a viable source for psilocybin. Cactus plants might contain other psychoactive compounds, such as mescaline, but they do not produce psilocybin. Thin air is not a source for any organic compounds, and corn stalks are generally not associated with psychedelic substances. Thus, the identification of certain mushrooms as the source of psilocybin is accurate and supported by extensive research in both the fields of botany and pharmacology.