San Pedro Cactus Identification

San Pedro cactus is a spiny succulent that grows in the desert and is known in both North and South America as a primary source of the psychedelic substance mescaline (along with the peyote cactus), which is harvested by squeezing out the juice or cutting and preparing the thick skin of the plant.

The cactus was believed to have been used by native South American tribes for religious rites dating back thousands of years, and was given the name San Pedro, or Saint Peter, by Spanish missionaries because it appeared the Peruvian shamans treated the plant as if it, like Saint Peter, held the keys of heaven. While the San Pedro cactus may be confused with other similar plants, its size and growth habits tend to give it away. There are about 30 different species of San Pedro cactus.

The San Pedro cactus is columnar in shape, which means that it grows up in a straight pillar, generally ballooning out slightly at the top of the plant. They can reach from a few inches to a foot or more in diameter at the base, and grow around one foot a year if conditions are hospitable. Plants as tall as 20 to 30 feet and more have been recorded. They may also produce a number of arms in a brush-like fashion as they grow, although this is more common after several years of growth and should not be used as a vital identification marker.

The San Pedro cactus starts with a sage-blue tint, which it often keeps at the base as it grows, but is replaced by a more common green shade at the top of the plant. The cactus is vertically ribbed, or divided into several different sections around the column, each with a row of spines to discourage predators. Most plants have six to eight ribs. The flowers of the San Pedro cactus are especially noticeable--they bloom large and white from the top of the cactus.

Originally the San Pedro cactus hails from the South American mountains, growing naturally in Peru, Bolivia, Chile, Ecuador and other countries near the Andes mountains. It gradually spread to the desert areas of North American as well, and in the era of modern travel it has spread to other locations throughout the world, notably desert or tropical areas such as Hawaii. The spread of San Pedro cactus, which followed the use of the drug mescaline, caused many countries, including the U.S. and Canada, to prohibit the use of mescaline and the growth of San Pedro cactus for any use except ornamental purposes.