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Ariocarpus is the genus name for approximately six to eight species of slow-growing cacti. These cacti have thick rootstocks and conical, unbranched stems, giving them an appearance similar to that of rocks. In fact, they tend to blend in with the rocks and soil in their native lands of Mexico and the US state of Texas. As a result, Ariocarpus has adopted the common name, living rock.
The various species of cacti in the genus Ariocarpus are typically spineless, and they have flowers in the winter and fall months. Depending on the species, the flowers can be purple, red, yellow, pink, or white. Most species also have green berries with black seeds, and they grow best in desert climates. In fact, some botanists believe that they can bring their roots closer to the surface of the soil during periods of extreme drought. This survival mechanism may allow them to find water more easily.
The majority of the species of cacti that fall in the genus Ariocarpus can be grown either outside or in a greenhouse. If they are grown in a greenhouse, they should have potting soil designed for cacti. In addition, they require full light. During their growing season, they require moderate water, but when the growing season is over, they require only minimal water. If they are grown outside, they need full sun and poor, infertile soil that drains well.
One species of Ariocarpus, A. fissuratus, is also known by its common names, Chautle living rock and false peyote. It is a flat-topped cactus that has blunt, gray-green tubercles or wart-like projections. In the fall months, it has pink or magenta flowers. The living rock grows low to the ground, much like a rock, and only reaches 4 inches (about 10.2 cm) tall.
Another species of Ariocarpus, A. retusus, is also flat-topped with gray-green tubercles. The difference is that it produces white and pink flowers in the fall months. In addition, it lays even lower to the ground than A. fissuratus, reaching heights barely over 3 inches (about 7.6 cm). A third species of Ariocarpus, A. trigonus, is slightly taller at 5 inches (about 12.7 cm). This flat-topped, rock-like, cactus has yellow flowers.
Interestingly, Ariocarpus are actually endangered. Fortunately, since they are quite rare in the wild, they come equipped with a natural defense mechanism. The cacti contain toxic alkaloids. The alkaloids are bitter to the taste. As a result, it protects them from consumption by cattle, sheep, deer, and other herbivores.
When I think of the term "living rocks" I think of the cactus species known as lithops, rather than this one. This one is nice and I can see why they are called "living rocks" especially since they live so long, but they still look like a succulent to me.
While the lithops species of cactus really does look like a fleshy rock or maybe a bit of coral reef, and just blends in with the other rocks until they put out their flowers which look a bit like daisies.
I guess this one lives in Mexico and the lithops live in Africa, so they are quite distinct, but it can still be confusing.
This kind of cactus grows very slowly, so if you want one that will establish itself more quickly in your garden, you might want to consider getting an ariocarpus which has been grafted onto another kind of cactus root stock.
This works in kind of the same way as when they graft fruit trees onto different root stock, enabling the plant to take on some of the abilities of the roots.
In this case, it makes the cactus grow faster, or sometimes it's to make them less vulnerable to damage.
Unfortunately, they don't always turn out to look like they would if they were ungrafted, so you might want to do with this some caution.