The hallucinogen mescaline is derived from:

Mescaline is a naturally occurring hallucinogen that is primarily derived from the peyote cactus, which is native to parts of Mexico and the southwestern United States. This cactus, specifically Lophophora williamsii, contains various alkaloids, with mescaline being the most notable for its psychoactive properties. The use of peyote as a psychoactive substance has historical significance among many indigenous cultures, especially in religious and ceremonial contexts.

In contrast, the other options do not contain mescaline. The coca plant is known for producing cocaine, and the sage bush refers to plants like sagebrush, which do not contain hallucinogens. Mushrooms can contain different psychoactive compounds, such as psilocybin, but they are not related to mescaline. Thus, identifying the peyote cactus as the source of mescaline is crucial for understanding the pharmacological and cultural relevance of this substance.