How to Tell the Difference Between Penis Cactus Varieties

This is the Trichocereus bridgesii monstrose, also known as the Penis Cactus. But did you know there are actually two types of Penis Cactus? In this guide, we’ll break down the differences between the short form and long form cacti, covering everything from their physical traits and growth habits to care requirements and propagation tips.

What Is Trichocereus bridgesii monstrose?

Trichocereus bridgesii monstrose, or TBM for short, is a beloved member of the San Pedro family. It originates from a naturally occurring mutation of Trichocereus bridgesii, also known as the Bolivian Torch cactus, which is native to the high-altitude regions of Bolivia. This columnar cactus is known for its fast growth, slender green stems, and distinctive long yellow spines, key traits that you can definitely recognize that are carried over into the TBM.

To add to the craziness there are 2 distinctive forms of TBM, short form and long form, which are also referred to as TBM Type A (long form) and TBM Type B (short form).

Physical Differences: How to Identify Short Form and Long Form Penis Cactus

The penis cactus comes in two varieties, short form and long form cultivars. These cultivars refer to plants that have been propagated usually through cuttings to produce genetically identical offspring, ensuring new plants continue those desired traits. The distinctions between the two can be hard to observe as young plants but as they grow into mature cacti you’ll notice a few differences. 

Short Form (Type B)

The short form monstrose Trichocereus bridgesii, or Type B, is the most common variety and is easily recognized by its more compact and rounded nodes. Each segment typically measures 2 to 3 inches, and the plant grows quickly, often adding 1 to 2 nodes per season. The short form has less prominent areoles and shorter, more frequent spines.

Unlike its long form counterpart, this TBM variety remains shrubbier overall, forming small clusters at the base and frequently branching off to produce offsets. Because of the more frequent offsets the plant has a tendency to crowd itself and grow more outward as it matures. Mature plants can reach heights of 3 to 4 feet and spread up to 5 feet in diameter. 

Long Form (Type A)

The long form penis cactus is a more rare cultivar and has distinctively elongated nodes compared to the short form, which typically range from 4 to 8 inches and sometimes longer. They are characterized by elongated stems that branch less frequently, with fewer areoles forming primarily at the base, and more sparse spines compared to the Type B. 

These cacti grow more slowly than the short form and grow predominantly upright, with mature specimens reaching a diameter of 3 ft and heights of around 3/4 feet. This unique combination of features makes them a highly sought-after addition to any collection.

The description above is for the predominant cultivar of long form in the United States. However in our collection & various collections we’ve noticed 2 additional distinct forms:

• Extra long form - showing crazy long branches around 1-2 feet upright 

• Prostrate extra long form - grows 3 ft snake-like arms on the ground. 

Caring for TBM Type A vs. Type B

Care requirements for long form and short form penis cacti are largely similar. Both bridgesii require bright light for at least 6 hours a day, both need a well-draining soil mix with approximately 70% inorganic material, and both need good airflow and preventative fungicide treatments. More in-depth care instructions can be found on our Penis Cactus 101 Blog.

That being said here are few small differences in their care requirements:

• While both forms of TBM have fungal issues, the Long form penis cactus is more fungal prone, so observe your cacti often for any signs of fungal issues and take preventative measures by:

• Using more inorganic material in your potting mix - 70/30 pumice to coco or peat moss

• Promoting good airflow 

• Allowing fully dry periods between watering 

• Fertilizing in spring and summer - a strong plant is less susceptible to issues

• And Using plastic pots (help with airflow vs terracotta)

  

If things take a turn for the worse, a fungicide can help your cactus recover. Early detection and good care are your best defense!

• It is especially important when propagating long form penis cacti to both take and leave areoles when taking cuttings. Because of their fewer areoles and less frequent branching you have to be more careful where you cut because they won’t be able to grow new offsets without areoles.

  

• Because the short form tends to crowd with many offsets they can poke each other and may benefit from some pruning of inner nodes on mature plants.

Which Penis Cactus Is Right for Your Collection?

To summarize, the penis cactus is a monstrose mutation of the bolivian torch cactus, Trichocereus bridgesii, and comes in two main forms. The long form (Type A), is recognized for its elongated, less frequent nodes, and the short form (Type B), is known for its compact, rounded segments. Care is generally the same for both types of TBM but the long form tends to need more preventative fungal care, and requires more careful propagation.

Now that you know the differences, you’ll be able to care for and appreciate these unique plants even more. Whether you’re team short form or long form, one thing’s for sure—there’s nothing quite like a Penis Cactus to steal the spotlight in any collection!