Cactus containing Mescaline. Interesting compound. Also found in peyote. San Pedro grows everywhere and you've probably seen it around. Another one to look for is Peruvian Torch.

Peyote grows extremely slow and only in small corners of the world, I'd recommend skipping them as they need to be protected.

San Pedro grows about 40cm a year where I live. They can take plenty of water (growing thin and long) or they can get by with a cup a month (growing shorter and thicker). I'd recommend starving them once in a while to stress them out - this makes them produce mescaline. They also produce wonderful huge white flowers (only for a short time each year). If you do end up growing them, never sell them. Always give cuttings away as gifts to others.

Read up a bit about mescaline, it is not like the other psychedelics. With mushrooms, dmt, lsd + lsa (seed from Argyreia nervosa - plenty gardens have them) - these are all similar compounds with similar effects. Mescaline's effects are a bit different, so worth it to explore even if you think you've seen it all.

Fun fact: Mescaline is mentioned in The Matrix (the first one) when Neo encounters the girl with the white rabbit tattoo...make of it what you will.