The battle between prey and predator has been going on since the beginning of time. In the animal kingdom, prey evolved defenses like camouflage, aposematism and mimicry to protect themselves from becoming a meal. Much study has been done in the animal kingdom on the use of camouflage as a defense mechanism. In the plant world, it was a seldom studied area and until more recently, and was rarely written about. I am not sure why. But the use of camouflage in the plant kingdom certainly does exist as a means of anti-herbivory defense. I recently viewed one genus that has evolved to become an expert of camouflage in habitat while on my trip around Monterrey, Mexico. That genus is Ariocarpus. And as you will soon see, the anti-herbivory camouflage of Ariocarpus scapharostrus and Ariocarpus kotschoubeyanus is remarkably impressive.

For those who have not heard of the genus Ariocarpus before, you may know them from their common name – “Living Rocks.” The common name comes from their appearance of a body of discolored tubercles which make them virtually impossible to spot in habitat. All of the eight recognized species of Ariocarpus grow semi-buried and often do not rise above ground level at all, which can give them the appearance of being “living rocks.” Ariocarpus are found as far north as the Chihuahuan Desert in Texas, all the way down towards Queretaro, Mexico. They have become a favorite of the cactus and succulent collector, so much so that some localities are under great pressure from poachers due to the immense popularity of the plant. Their growth is slow, and the unscrupulous collector’s desire to have ancient plants in their collections has threatened many species.

Ariocarpus are true cacti; however, without spines, they must rely on their nondescript appearance to camouflage themselves in their native habitats. To me, the most impressive example of this camouflage in Ariocarpus comes from the species Ariocarpus scapharostrus. Ariocarpus scapharostrus has the narrowest range of all Ariocarpus and can only be found in one small valley just outside the town of Rayones in the state of Nuevo Leon. Ariocarpus scapharostrus is a protected species that resides on private property. To see it, we had to first get permission from the land owner and then hopped a barbed wire fence to walk up the hill seen in the top right in the photo below.

Cactus hunting extraordinaire, and my guide for the four days around Monterrey, Miguel González Botello at the top of the hill where we would find Ariocarpus scapharostrus. Got to love cactus hunters. They always come so well prepared. Miguel is sporting two cameras around his neck, an iPhone and diffuser at the ready. The cactus in front is an Echinocactus platyacanthus.

Here is the top of the exposed limestone shale habitat where Ariocarpus scapharostrus grows. 

Eagle-eyed Miguel had already spotted plants but he wouldn’t tell me where. He wanted me to try and find them on my own. Kind of like an Easter egg hunt, only these eggs have evolved over millions of years to hide from herbivores. There is one “Living Rock” in the photo below. Can you spot it?

Let’s zoom in. Can you see it now?

You don’t? Yeah, don’t feel bad. Neither could I at first. In both the photos, the Ariocarpus scapharostrus can be found dead center. Here, let me help you. After you see it once, you will know what to look for in future photos in this blog post.

Anti-herbivory camouflage at its finest. Both the shape and color of Ariocarpus scapharostrus tubercles blend perfectly with the surrounding limestone gravel. What herbivore could find that?

Here is one that is easier to see, as its tubercles stick out farther than most Ariocarpus scapharostrus that Miguel and I found. The second photo has my wedding ring for scale.

The small Ariocarpus scapharostrus below is exposed to show the plant’s woolly apex from which new tubercles and flowers emerge. When the plant is in bloom, it ironically sticks out like a sore thumb, as brilliant magenta flowers contrast with the dull, gray color of the limestone gravel. I was visiting outside blooming season so I can’t show you a picture of one in flower. However, an early blog post of mine on the closely related species Ariocarpus agavoides in bloom will give you a better idea what the flowers look like.

Going back to the matter of anti-herbivory camouflage, prior of my leaving for Mexico and upon my return, I attempted to do some basic research on the subject. I found it extremely difficult to find anything to read about it. There are volumes of writings about anti-preditory camouflage in animals. You can also read about other forms of plant defense against herbivory outside camouflage. The subject of plant anti-herbivory camouflage appears to be a newer one. Documentation starts around the 1970s. And only within this last decade has more research been done. The best source out there is contained in a recently published book by Simcha Lev-Yadun, titled “Defensive (anti-herbivory) Coloration in Land Plants.” Thanks to Google Books, I was able to read the sections on camouflage. I bring all this up because I find it odd more hasn’t been written on the subject. Especially when you see a plant like Ariocarpus scapharostrus so perfectly evolved for an extremely distinct habitat. The color and shape of the plant could barely be more perfect if drawn up in a lab.

Look at Ariocarpus scapharostrus from directly above. It is more impressively camouflaged from this angle.

Metaphor time! I arrived a white belt in Ariocarpus scapharostrus hunting, but after a few hours, I left a black belt. Once you know what to look for, the small imperfections in the limestone gravel hills got easy to spot when you got down low and looked out across the ground. Evolution isn’t perfect.

Two plants in the photo below.

Miguel and I still had a long day ahead of us plant hunting, so we packed it up earlier than I would have liked. You can read more about our trip this day by clicking here. Before I close out in this locale, I thought I would leave you with a challenging Ariocarpus scapharostrus to search for in the photo below. Yes, there is a plant in the picture. I am not playing some cruel joke on my readers.

The second locale I would visit was that of Ariocarpus kotschoubeyanus. Ariocarpus kotschoubeyanus can be found in quite a few small populations around northeast Mexico. Miguel would take me to a location just outside the small pueblo of Mina in Nuevo Leon. Ariocarpus kotschoubeyanus grows in limestone silt plains and dried mudflats. A totally different habitat than the exposed limestone shale Ariocarpus scapharostrus is found.

For me, Ariocarpus kotschoubeyanus was easier to spot than Ariocarpus scapharostrus. Still, Ariocarpus kotschoubeyanus has evolved an impressive camouflage to blend into its environment. It should be easy to spot in the photo below. If you can’t see it, look for the stick pointing to it. The second photo shows a closer view of the same plant.

Ariocarpus kotschoubeyanus has quite a few characteristics that make it unique from Ariocarpus scapharostrus. The differences prove much better for blending into the dried limestone mudflat like shown above. The two main differences are that 1) Ariocarpus kotschoubeyanus tubercles lie flat on the soil surface versus the erect tubercles of Ariocarpus scapharostrus, and 2) Ariocarpus kotschoubeyanus has a wooly, areolar groove on the tubercle, whereas the Ariocarpus scapharostrus tubercle is wooly-free and groove-less. As we saw with Ariocarpus scapharostrus in the first part of this blog post, the erect, wooly-free and groove-less tubercles do an impressive job of hiding it in limestone gravel but those features would make it stand out in the limestone mudflats. As you saw above, Ariocarpus kotschoubeyanus with the flat tubercles and wooly groove to collect limestone silt is a much better camouflage in the mudflats.

To better prove this, I give you the two photos below. It confirms how well the flat, wooly-grooved tubercles collect the limestone silt to hide in the landscape.

To further illustrate this, look at what a Ariocarpus kotschoubeyanus looks like in cultivation away from the limestone silt.

Below is a really nice Ariocarpus kotschoubeyanus blending in with its environment. My wedding ring is used for scale in both pictures.

Another angle of the same Ariocarpus kotschoubeyanus shown above. This plant was the most attractive and largest of the ones we found all day. Poachers have removed the large, old specimens over decades in this locale. Lucky for these plants, like the one above, it is now easy to buy seed-grown Ariocarpus kotschoubeyanus at this size online or at your favorite speciality succulent nursery. So plants like this shown above are usually safe. For now…

Anti-herbivory camouflage in the dried, cracking mudflats.

Two Ariocarpus kotschoubeyanus in this photo.

An example of a more exposed Ariocarpus kotschoubeyanus. Much easier to spot when they are not lying flush with the soil level.

Another cactus that was pretty prevalent in the limestone mudflats was Lophophora williamsii (Peyote).

While it wasn’t flowering season for any of the Ariocarpus I would see, it was for Lophophora williamsii.

You can clearly see that Lophophora williamsii didn’t evolve any anti-herbivory camouflage. However, it uses another defense against consumption by herbivores. Lophophora williamsii has high levels of a few different toxic alkaloids, such as hordenine. Interestingly enough, so does Ariocarpus. Not only did Ariocarpus evolve to hide extremely well in their environments, they also have a backup defense, in that if eaten, the herbivore won’t be feeling very well soon after.

I never would have expected Mammillaria heyderi to also grow right at the soil level in a similar fashion to Ariocarpus, but it does. The difference is that Mammillaria heyderi has spines as its main defense against getting eaten.

The third and final locale I would visit was that of Ariocarpus trigonus. It can be found growing in limestone as well, usually in limestone gravel or scree, but like shown below, it does well in exposed limestone soil.

Ariocarpus trigonus is one of the largest growing of all Ariocarpus and can grow to over a foot wide given time. It can be found at some locales within large colonies, but the locale we visited was not far from the Monterrey International Airport and didn’t have any large representatives thanks to poachers. Ariocarpus trigonus grows very similarly to what we saw in Ariocarpus scapharostrus. However, the longer and pointier tubercles of Ariocarpus trigonus were much more exposed, making it much easier to spot in habitat.

This small plant below was the only other Ariocarpus trigonus Miguel and I would find. To be fair, we only spent 20-30 minutes looking, as we still had a lot planned on the day (which seemed to be a common thread each day in Mexico).

So what do you think? Pretty impressive examples of a plant using anti-herbivory camouflage, wouldn’t you agree? While Ariocarpus isn’t alone in its anti-herbivory camouflage, you would be hard-pressed to find better examples. Lithops and some Haworthia from South Africa come to mind. However, to see them in habit involves days of travel to reach them from San Diego. Ariocarpus are just a day’s drive or a short flight from San Diego.

Tagged: Cactus, Mexico, Travel

May 11, 2017