How to Easily Identify the San Pedro Cactus

The San Pedro cactus, or Trichocereus Pachanoi, is an iconic cactus, known not only for its stunning appearance but also for its cultural significance. However, identifying this cactus out in the wild can be a challenge, especially when other species might be easily mistaken for it. In this guide we are going to teach you how to identify a San Pedro cactus by its physical appearance and compare it to a few common cactus imposters. 

A Quick Note

As a quick note, we are going to be sticking to Trichocereus Pachanoi, commonly known as the San Pedro, for identification. If you’re interested in distinguishing between the other main types of Trichocereus cacti you can check out our other guide here.

Context Matters

When identifying cacti, it's important to think about the context in which you’re looking at a plant. For example, a fully mature cactus might look different than when it was very young, and a weathered cactus will look much different than one kept in pristine conditions (proper watering frequency, fertilizer application, pest management, etc). Different growth forms and hybrids can also carry different qualities and physical characteristics to further throw you off. Keep this in mind when starting your identification process.

Identifying San Pedro: Physical Features

When examining a cactus for identification, you can look at these physical features to confidently distinguish a San Pedro cactus from others:

• Stem/Body Features: San Pedro cacti have a more rounded shape at the tip and ribs, and are more prone to forming a lot of offsets from their base once matured. They are fast growers with “strict upright growth”, can get up to about 20-30 ft tall, and have a medium thickness compared to other cacti.
  
• Skin Features: The color of the skin will range from light green to dark green, and will sometimes be a more glaucous blue-green color. The texture of its skin will typically be smooth rather than grainy.
• Rib Features: San Pedro cacti typically have between 5-8 ribs that are more rounded in shape rather than pointed and thin.
• Areole Features: The areoles of San Pedro cacti will be smaller and a grayish white in color. V-shaped notches will appear right above each of the areoles.
• Spine Features: San Pedro spines are short and golden-brown. Typically they will number between 2 and 10 spines per areole.
  
• Flower Morphology: The San Pedro cactus has large, white, night-blooming flowers that are covered with black and brown hairs on the outside.
  

*for more info on anatomy of SP cactus check out our guide here!

Popular San Pedro Imposters

Now that we know the physical characteristics of a San Pedro cactus, let’s look at the five most common San Pedro imposters and compare them to the real thing.

1. The Peruvian Apple Cactus (Cereus spp.). This cactus is the most commonly confused San Pedro imposter! They’re similar in their columnar growth, size, profile, color, and flowers, but where the San Pedro has more strict columnar growth, the Peruvian Apple will spread out and branch like a tree. The Peruvian Apple has markedly skinnier ribs, and their flowers are also hairless.
   
2. The Mexican Fence Post (Pachycereus marginatus). This cactus is similar in size, profile, and color, but the main difference is that the Mexican Fence Post has unique vertical stripes of spines along it’s body. It also has much smaller pink flowers.
   
3. The Blue Torch Cactus (Pilosocereus). This cactus can have a similar blue-green color that the San Pedro has, but its ribs are much more well defined and it’s spines are much more thin and bright yellow. They tend to get hairy at the tips, and they also have small white tube-like flowers.
   
4. The Blue Candle Cactus (Myrtillocactus Geometrizans). This cactus is also similar in color to bluer san pedro, with shorter spines. To tell this apart from a San Pedro, notice that the Blue Candle has black spines rather than golden brown ones. They tend to form branches higher up and do not stick to strict upright growth, and have very small, white, petal-like flowers.
   
5. The Toothpick Cactus (Stetsonia Coryne). This columnar cactus is similar in color to the San Pedro, but has much larger woolen areoles, and several long toothpick-like spines coming out of each areole.
   

6. Other Imposters: 

• Stenocereus and Polaskia species: Look for thinner, more acute ribs, and an oval-shaped central spine.
• Browningia hertlingiana: Focus on the wavy ribs and often more than 8 ribs in mature plants.

Conclusion

Identifying the San Pedro cactus requires attention to detail and an understanding of its unique traits. Each cactus is a masterpiece, and recognizing these distinctions enhances the enjoyment of these natural wonders. Whether exploring the wild or cultivating a collection, this guide equips you to differentiate the San Pedro from imposters, fostering a deeper appreciation for its beauty and individuality. Use this resource to confidently navigate the world of cacti and hone your identification skills. Enjoy the journey!

Key Takeaways

• Trichocereus cacti are primarily defined by: tall green or green-blue columnar growth with vertical ribs, variable spines and a strong tendency to branch and form candelabra-like structures that showcase large hairy night-blooming flowers. 
• When identifying San Pedro cacti, it's important to recognize that various factors such as age, conditions, and growth forms can influence the appearance of a plant.
• When examining a San Pedro variety for identification, look at these features to confidently distinguish a Trichocereus from other cactus: stem/body, skin, ribs, areoles, spines, and flowers.
• Popular imposters of the San Pedro cactus are: the peruvian apple, the mexican fence post, the blue torch, the blue candle, the toothpick cactus, the stenocereus and polaskia species, and the browningia getlingiana.