There are many cacti in several genera that produce mescaline and similar phenethylamines in varying amounts. Cacti with a history of human use include Peyote (Lophophora williamsii), San Pedro (Trichocereus/Echinopsis pachanoi), Peruvian Torch (Trichocereus peruvianus/Echinopsis peruviana), Bolivian Torch (Trichocereus bridgesii/Echinopsis lageniformis), and Trichocereus/Echinopsis scopulicola. Mescaline also occurs in other common cacti in trace amounts. The concentration of mescaline and other alkaloids varies considerably between between species and individual plants. Other alkaloids found in psychedelic cacti include 3,4-dimethoxyphenethylamine, 4-hydroxy-3-methoxyphenethylamine, 3-hydroxy-4,5-dimethoxyphenethylamine, 4-hydroxy-3,5-dimethoxyphenethylamine, anhalonidine, anhalinine, hordenine, tyramine, and 3-methoxytyramine. The green skin of the cactus is where the majority of psychoactive alkaloids are located.