Mescaline, along with other alkaloids are found in the peyote cactus, mescaline alone is a different experience than peyote. Similarly there are a few other cacti that contain mescaline (not quite as much, but enough) and grow at a MUCH faster rate than peyote, i'm not going to go into detail as to their names but i will say they are legal where i live, and a good trip.
check out this link
Erowid Peyote Vault : Peyote and other Psychoactive Cacti
I suggest reading this top to bottom to find out about cacti that are psychoactive.
Also, i have pretty much read erowid top to bottom, there are lots of things that are psychoactive (other than cacti).
If you're trying to find out about a drug you're about to take or wanted to find out if the rumors about it i cant stress how good of a resource this site is.