How to Identify Different Types of San Pedro Cactus 

With over 20 species of Trichocereus cactus listed, identifying these statuesque columns from South America present a complex puzzle, challenging even seasoned collectors. Their subtle differences and unique characteristics turn the identification process into an engaging exploration. This straightforward guide is designed to give you the tools you need to confidently identify the major San Pedro varieties.

In the following sections, we'll break down the characteristics of five most common San Pedro cactus types: Trichocereus pachanoi (San Pedro Cactus), Trichocereus peruvianus (Peruvian Torch Cactus), Trichocereus bridgesii (Bolivian Torch Cactus), Trichocereus scopulicola (Scopulicola Cactus), and Trichocereus terscheckii (Argentine Saguaro Cactus).

Whether it's providing the perfect care, understanding their hidden secrets, or simply marveling at their unique beauty, accurate identification turns the seemingly mundane task into an exciting journey of discovery. It's more than a hobby; it's a pursuit of knowledge that resonates with the heart and mind of every true cactus collector.

How to Identify a Trichocereus Cactus 

Before we delve too deeply, let's ensure we're looking at the right Genus or family of plants. While columnar cacti might look similar at a distance, it's important to recognize the key factors that distinguish the Trichocereus genus from other columnar cacti. Trichocereus cacti are primarily defined by tall green 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. 

Context Matters.

When identifying San Pedro cacti, it's important to recognize that various factors can influence the appearance of a plant. These factors can provide essential context and insights into the traits that distinguish different types of cacti. As you embark on your identification journey, keep these key contextual elements in mind:

Age: Younger plants often exhibit traits that might not align with the typical characteristics of their mature counterparts and can be more difficult to distinguish. Mature plants are typically easier to identify since they express well defined characteristics. Use our guidelines as a general direction, but allow room for these age-related differences. 

Conditions: The environment in which a San Pedro cactus is grown significantly influences its appearance. Factors like whether it's potted or in the ground, the amount and quality of light it receives, and the care it's given all play a role in shaping its characteristics. Potted plants tend to be smaller and thinner, while those in the ground develop a thicker, branching structure. Light intensity affects the color of the skin and spine length and girth of the plant. Typically spine length, and girth will decrease in filtered light or shade like in a greenhouse and increase with exposure to full sun. Glaucous coloring can vary and is often brought about by shade, genetics, and found most prominently on new growth as a sort of sunscreen. 

Additionally, the way a plant is cared for—watering frequency, fertilizer application, and pest management—can impact its health and, consequently, its visual traits. A plant in optimal condition will exhibit different qualities compared to one that's struggling due to poor care.

Growth Forms and Hybrids: San Pedro cacti exhibit a wide range of forms including monstrose (twisted or contorted growth), crests (wavy or fan-like growth), and seed grown hybrids that can introduce unique phenotypes. Some cacti might even display variegation, where parts of the plant exhibit different colors. While this guide primarily focuses on identifying columnar cactus, these different forms can carry certain qualities, such as areole size & color, spine color & structure, and skin color that are consistent in all forms.

Quick Field Reference Guide 

When examining a San Pedro variety for identification, follow these factors to confidently distinguish among them:

Stem/Body Features: Just as no two humans are alike, each cactus has its own distinct body shape and size. Take into account the overall dimensions of the plant, focusing on both its height and the girth of the stem. The plant's general form, its propensity for branching, and the shape of its tip can all serve as identifying markers that help differentiate various species.

1. Height vs. Age: When evaluating plants of similar age and under comparable growing conditions, height and growth rate are closely linked. While these cacti may ultimately reach similar maximum heights, they'll get there at different paces.
2. Stem Thickness: Ranging from Skinny to Average to Fat
3. Branching: Present or Absent? Number of Branches? Origin of Branching?
4. Tip Shape: Rounded vs. Angular
5. Side Profile: Smooth or Sawtooth-like

Skin Features: Take a close look at the color and texture of the cactus's skin. You'll typically encounter a spectrum from bluish-green to vibrant or deep green tones. Whether the skin is smooth or has a grainy texture can be a defining characteristic to differentiate between certain varieties.

1. Color: Ranging from Light Green, Dark Green, Glaucous, or Blue.
2. Texture: Smooth vs Grainy

Rib Features: Take note of the rib count and the shape viewed from the top of the cactus stem. While counting ribs isn't a foolproof identification method, it can assist in categorizing based on species tendencies. For Trichocereus cacti, you'll generally find 4-18 ribs.

1. Rib Count: Usually falls within the 4-18 range
2. Rib Shape: Characterized as either Rounded or Sharp/Angular

Areole Features: Examine the areoles—those specialized circular pads where the spines emerge. Pay attention to their color, any notching or indentations above them, their size, and their shape. When combined with the morphology of the spines, these areole characteristics serve as a sort of "fingerprint" for the cactus, aiding in its identification.

1. Color of Pad: Ranges from White to Gray, or from Golden to Brown.
2. Notching: Check for V-Shaped Notching above the areole.
3. Size: Can vary from Small to Medium to Large, ranging from a few millimeters to a few centimeters.
4. Shape: Take note if they are Round or Oval, and whether they appear Sunken, Swollen, or Flat.

Spine Features: Spines can show considerable variation in length, number, and color across a single cactus plant. It's best to consider these characteristics as an average across the whole plant and in relation to the areoles for more accurate identification. Focus on the average length of the spines and the color of new spines emerging at the growth tip. Also, tally the average number of spines per areole and observe any unique arrangements, which we refer to as the "spine constellation."

1. Spine Length: Categorized as Spineless, Short Spine, Medium Spine, or Long Spines.
2. Spine Color at Tip: Varies from Golden Brown to Yellow, Gray, or Black.
3. Average Number of Spines per Areole: Typically ranges between 1 and 12.

Flower Morphology: If you're fortunate to observe your San Pedro cactus during its blooming cycle, the flower characteristics can be an invaluable seasonal tool for identification. Take note of any distinctive hairs on the flower buds, as well as the colors present on those buds, axils, or the flowers themselves. These traits can help you distinguish between specific species within the San Pedro cactus family.

1. Flower Color: Typically White or Colored
2. Hair Color on Buds: Ranges from Black/Dark to Brown or White/Light

With these factors in mind, you'll have a step by step guide to confidently identify and appreciate the diverse San Pedro cactus varieties that grace your collection. Let’s dive into the specifics of the major types of San Pedro Cactus now.

Decoding the San Pedro Varieties:

San Pedro Cactus | Trichocereus pachanoi | Echinopsis Pachanoi: The iconic San Pedro cactus stands tall, with ribbed stems reaching impressive heights. Native to the Andes Mountains of Peru and Ecuador, this cactus thrives in altitudes of 2,000 to 3,000 meters above sea level and can grow to be between 20 to 30 feet tall. Its vibrant green hue, golden-brown spines, and enchanting white flowers that blossom under the night sky make it an exquisite addition to any collection. 

Its natural habitat poses diverse weather conditions, including fluctuating temperatures, strong winds, and varying levels of rainfall. This versatility allows the San Pedro to adapt and flourish in an array of climates, making it an incredibly resilient and adaptable cactus.

•    Geographic Habitat: Andes Mountains of Peru and Ecuador
•    Identification: 
• Body
• Height: Tall - Fast Growing
• Girth: Medium Thickness
• Shape: Rounded Shape at ribs and tips. 
• Branching: Prone to forming lot of branches once matured
• Side Profile: Distinctive notching can give a sawtooth like appearance. Others may have a more smooth club-like shape. 
• Skin
• Color: Dark Green, Light Green, Glaucous Blue.
• Texture: Smooth
• Ribs:
• Count:  5-8 Ribs typically
• Shape: Rounded
• Areoles: 
• Color: White to Gray
• Notching: V-Shaped Notches above the areoles
• Size: Small to Medium
• Shape: Round
• Spines: 
• Length: Short 
• Color: Golden Brown
• Number: 2-10
• Flowers: 
• Color: Large White Night-Blooming Flowers, 
• Hairs: Black to Brown hairs. 

Peruvian Torch | Trichocereus peruvianus | Echinopsis peruviana: The mystifying Peruvian Torch displays hues of blueish-green, longer spines that protrude fiercely from larger areoles. This slower growing cactus hails from Peru, predominantly in the Matucana region, thriving at altitudes of 1,000 to 2,500 meters above sea level. Its ability to adapt to coastal deserts and high-altitude mountain regions adds to its resilience and allure. It is the closest relative of the San Pedro Cactus.

When differentiating short-spined Peruvian Torch from San Pedro, a touch of caution is advised. Resemblances between these two species may emerge due to shared characteristics and potential hybridization, driven by their geographical overlap. Skin color, spine length, and the recognizable V-shaped notches usually serve as markers to distinguish between the two. However, given the diversity within each species, definitively telling apart short-spined peruvians from long-spined pachanoi can prove challenging even for experienced collectors.

• Geographic Habitat: Andes Mountains and Coastal Deserts of Peru 
• Identification: 
• Body
• Height: Tall - Slower Growing
• Girth: Medium to Large Thickness
• Shape: Rounded Shape at ribs and tips. 
• Branching: Prone to forming lot of branches once matured
• Side Profile: Smooth club-like shape with strong spines
• Skin
• Color: Bluish Green, Glaucous, Light or Dark Blue
• Texture: Smooth
• Ribs:
• Count:  6-9 Ribs
• Shape: Rounded
• Areoles: 
• Color: Brown, Beige, Golden
• Notching: Typically no V-Shaped Notches above the areoles
• Size: Large
• Shape: Round
• Spines: 
• Length: Medium to Long 
• Color: Honey colored or Brown
• Number: 6-8
• Flowers: 
• Color: Large White Night-Blooming Flowers, 
• Hairs: Black to Brown hairs. 

Bolivian Torch | Trichocereus bridgesii | Echinopsis legniformis: Gaze upon the elegant Bolivian Torch, its slender form graced by green skin and long yellow spines. This cactus calls Bolivia its home, flourishing at altitudes of 1,000 to 3,000 meters above sea level. Its adaptability to various climates, from semi-arid lowlands to high-altitude mountainous areas, underscores its elegance.

Spine length and color can vary quite a bit for this variety, in fact a short-spined Trichocereus bridgesii, is frequently mistaken for a pachanoi, earning it the name Auchuma. While distinguishing the two, you can rely on rib count, spine qualities, and the plant's overall shape. Pachanoi tends to have a rounded appearance at the tip with shorter spines and more ribs, while bridgesii boasts a pointed, sharply defined tip with longer spines and fewer ribs. Nevertheless, for the untrained eye, the resemblance between these columnar cacti is understandable.

• Geographic Habitat: Bolivia
• Identification: 
• Body
• Height: Medium to Tall - Very Fast Growing
• Girth: Skinny Thickness
• Shape: Sharp Angular Shape at Tip and Ribs
• Branching: Prone to forming lot of branches once matured
• Side Profile: Smooth Slender profile with sharp angular look
• Skin
• Color: Light Green to Vibrant Green to Glaucous
• Texture: Smooth
• Ribs:
• Count:  4-8 Ribs Most common with 4-6
• Shape: Sharp
• Areoles: 
• Color: White to Gray
• Notching: V-Shaped Notches above the areoles
• Size: Small
• Shape: Round to Oval
• Spines: 
• Length: Long
• Color: Yellow
• Number: 1-6 most classically 2-3
• Flowers: 
• Color: Large White Night-Blooming Flowers, 
• Hairs: White to Brown hairs. 

Scopulicola Cactus | Trichocereus scopulicola | Echinopsis scopulicola: Explore the charming Scopulicola, a nearly spineless cactus with dark green, grainy skin and plump growth. This cactus's original habitat spans regions in Bolivia only, thriving at altitudes of 1,000 to 1,500 meters above sea level. Its tenacity and ability to endure rocky, hilly terrains along with its enormous girth and nearly spineless appearance make it a unique member of the San Pedro family.

Most easily identified by its nearly spineless appearance Scopulicola can get confused for a San Pedro Cactus, but is best to rely on rib count and areole characteristics to distinguish it. 

• Geographic Habitat: Bolivia
• Identification: 
• Body
• Height: Tall - Average Growth Rate
• Girth: Large Thickness
• Shape: Rounded Shape at ribs and tips. 
• Branching: Prone to forming lot of branches once matured
• Side Profile: Convex look from extra girth and sunken areoles show as almost a dimple.
• Skin
• Color: Dark Green
• Texture: Grainy, like brail
• Ribs:
• Count:  4-6 Ribs
• Shape: Rounded
• Areoles: 
• Color: White to Gray
• Notching: Strong furrow or crease above the areole
• Size: Tiny
• Shape: Oval, Sunken or Depressed
• Spines: 
• Length: Nearly Spineless  
• Color: Gray, White
• Number: 3-6 Spines if any
• Flowers: 
• Color: Large White Night-Blooming Flowers, 
• Hairs: Black to Brown hairs. 

Argentine Saguaro | Trichocereus terscheckii | Echinopsis terscheckii, also known as "cardon grande," commands attention with its imposing stature that graces the arid landscapes of Argentina and Bolivia. This Saguaro of the South is a true giant and stands out from the crowd purely due to its size. In comparison to traditional saguaros found in the southwestern United States, the Argentine Saguaro showcases exceptional adaptability. It can endure colder temperatures during winters and is remarkably resistant to temporary frosts. Moreover, it thrives in hotter temperatures over time. Its faster growth rate in comparison to traditional saguaros makes it an excellent choice as a captivating centerpiece for any landscape. 

This cactus is sure to stand out with its enormous girth and long, dense yellow spines. You can distinguish it from San Pedro Cactus and others by its rib count, girth, and spine qualities most easily.  

• Geographic Habitat: Argentina & Bolivia
•  Identification: 
• Identification: 
• Body
• Height: Extra Tall - Slow Growing
• Girth: Extra Wide Thickness
• Shape: Rounded Shape at ribs and tips. 
• Branching: Solitary - Slow to form offsets only when matured
• Side Profile: Dense Spines alone the ribs
• Skin
• Color: Light Green
• Texture: Smooth
• Ribs:
• Count:  8-18 Ribs
• Shape: Sharp Ribs
• Areoles: 
• Color: White to Gray
• Notching: None, Dense Coverage
• Size: Large
• Shape: Round
• Spines: 
• Length: Long 
• Color: Yellow, Dense Clusters
• Number: 10+
• Flowers: 
• Color: Large White Night-Blooming Flowers, 

Understanding Cultivar Names, Hybrids & Genetic Diversity

It's key to grasp the concept that within the trichocereus genus an expansive realm of genetic diversity thrives. The interplay of natural hybridization and intentional crossbreeding has given rise to dozens of hybrids between various San Pedro Cactus Hybrids. This flourishing hybridization not only introduces exciting possibilities but also adds complexity that can challenge even the seasoned collector.

Central to this understanding is the realization that the cactus you encounter might be a hybrid creation, combining traits from two or more parent species. While the tools and guidelines provided offer valuable insights, it's important to acknowledge that without advanced techniques like DNA testing and comprehensive field analysis, absolute certainty remains elusive regarding the exact genetic makeup of a specimen.

In the realm of cacti taxonomy, a simple yet effective trend emerges as enthusiasts label hybrids as "pachanoid," "bridesoid," or "peruvionid" to denote specimens that skillfully blend distinct traits from parent species. "Pachanoid" hybrids embody Pachanoi's essence while echoing another lineage; "bridesoid" specimens proudly bear Bridgesii's form with subtle influences; "peruvionid" creations harmonize Peruvian Torch's qualities with another species. 

Even the most experienced cactus enthusiasts occasionally encounter situations where they must resort to the term "NOID," or “LOST LABEL” signifying a plant with No ID. Just as uncertainty remains an integral part of scientific exploration, it's prudent to retain an element of humility in our understanding of these remarkable plants.

With 15+ more species left off this list and countless hybrids it's important to note that this is not an exhaustive guide but one that will help you to identify the most common types you will see in collections, landscapes, botanical gardens or if you’re lucky enough worldwide cactus explorations!

Conclusion: 

In this detailed guide, we've delved into the intricate world of San Pedro cacti, providing you with the tools and insights needed to confidently identify five major varieties: San Pedro, Peruvian Torch, Bolivian Torch, Scopulicola, and Argentine Saguaro. Each of these cacti boasts distinctive traits that make them stand out in the vast landscape of Trichocereus genus.

As you wrap up your exploration into plant identification, keep this in mind: field science is rarely absolute. But that's no reason to shy away; we're all here because we're passionate about these unique cacti. While the world of taxonomy can lead to debates and nuanced discussions, don't let it sideline you from enjoying this fascinating hobby. Whether you're 100% sure of the identification or still double-checking, what's most important is your individual connection with your chosen cactus. So, with that said, let's jump into some key takeaways to solidify your newfound expertise.

Key Takeaways:

• Quick Reference Guide: When identifying a San Pedro variety, focus on size, shape, skin color, rib count, spine length, and areole characteristics for accurate differentiation.
• Contextual Clues: Age and environmental conditions influence a cactus's appearance, making it essential to consider these factors when identifying a specimen.
• Cultivars and Forms: San Pedro cacti exhibit diverse forms, including monstrose, crests, and seed grown hybrid phenotypes. These variations can introduce unique qualities that enrich the cactus landscape.
• Hybrid Complexity: The possibility of hybridization adds complexity to identification. While tools and guidelines are helpful, absolute certainty may require advanced techniques like DNA testing.
• A frequent practice involves labeling a cactus as "pachanoid," "bridesoid," or "peruvionid" when it's likely a hybrid but displays the dominant traits of one species over the other.
• Trust and Humility: While identification tools are valuable, it's essential to trust reputable sources and acknowledge the occasional uncertainty inherent in plant identification.

Citations & Resources

Britton, N.L. and Rose, J.N. (1919) The Cactacea Vol 2. Washington, DC: Carnegie Institute. 

Engel, L. (2023). The San Pedro Appreciation Guide, The Mescaline Garden, Tzanetis, S. (ed), Blue Mountains, Australia.

Knoll, P. (2016) The San Pedro Group. Patrick Knoll. 

Trout, K. (2005) Sacred Cacti 3rd Edition; Part B. Trout’s Notes on San Pedro & Related Trichocereus species . Mydriatic Publications.