Ariocarpus are among the oddest and most intersting of all cacti.  Their native habitat is northeastern Mexico and on into southern parts of Texas. Ariocarpus are unlike many other spherical or columnar cacti in that most of the main body of the plant typically grows underground. In habitat, often all that is seen is the many pointed star pattern formed by the elongated tubercles protruding from the ground. The top of the plant is often nearly level with the surrounding ground and thus can make these hidden plants very difficult to find, when not in flower.  Ariocarpus flower in the fall. The cryptic nature and roughed texture of these plants have earned them the nickname "Living Rocks".  Their habitat can reach extemely high temperatures throughout the summer, and so the plants have adapted to difficult conditions.

The Species

Ariocarpus were originally named by in 1838 by Michel Scheidweiler, a Belgian botanist. In 1839, however, Charles Lemaire published the name Anhalonium for the same plant genus. Lemaire’s reputation as an authority on cactus led to the widespread use of the name Anahalonium. It was not until around 1900 that the name Ariocarpus began to be accepted, based on its priority of publication. E.F. Andersen details the history of Ariocarpus in his excellent book The Cactus Family (© 2001). Lumpers and splitters still seem to be playing with what plants fall under the genus Ariocarpus. Andersen recognize the following six species in his new book. All species are listed in Appendix I of CITES.

Fig. 1 Ariocarpus agavoides   Mark Fryer
Photo: Ross Shumway

Ariocarpus agavoides

The tubercles are dark green to brown, elongated and thinner than other species, and the flower is magenta. A. agavoides is rare due to its occurance in only a few locations, and overcollection.

Ariocarpus bravoanus subsp. bravoanus, subsp. hintonii

A small rare Cites I plant, the tubercles are gray-green, flattened, and triangular. A. bravoanus is found only in a few localities and has a magenta flower.

Fig. 2 Ariocarpus fissuratus   Greg Wade
Photo: Ross Shumway

Ariocarpus fissuratus

The tubercles are flattened or convex, and usually have many fissures on top. This species is widespread in S. Texas and parts of Mexico. The flowers are magenta and this species can up to 6 inches in diameter.

Fig. 3 Ariocarpus kotschoubeyanus  var. macdowellii  Greg Wade
Photo: Ross Shumway

Ariocarpus kotschoubeyanus

This species is flattened and does not rise above ground level. This small species (< 3in), has flattened dark olive green tubercles with wooly furrows that run their length. It usually has magenta flowers, excepting one known population that has white flowers.

Fig. 4 Ariocarpus retusus  subsp. trigonus  Jerry Williams
Photo: Ross Shumway

Ariocarpus retusus  subsp. retusus, subsp trigonus

This is the largest species, to 12in in diameter, and projects above ground level. The pointed tubercles are usually smooth with areoles sometimes present at the tip. The subspecies retusus is widespread and have flowers that are cream or white, occasionally with reddish midveins. The subspecies trigonus is somewhat less widespread and the flowers are white to pinkish white.

Ariocarpus scaphirostrus

This small species has dark green to brown tubercles that are twice as long as wide and protrude nearly vertically from the ground. It has magenta flowers and occurs in only one valley.

Fig. 5 Ariocarpus grafted seedling   Mark Fryer
Photo: Ross Shumway

Cultivation

Ariocarpus have a reputation of being extremely slow and difficult to grow. This reputation seems to be only partly justified. Ariocarpus are slow growing but certainly not as slow as some other types of cacti. Andreas Laras (CSSA Journal Vol 71, No. 4), claims to have grown A. retusus from seed to 4 inches in about 5 years and has had several species flower in the 3 to 7 year time frame. Ariocarpus appreciate being grown in non-organic free draining soil like many other cacti. Some people have suggested that the addition of dolomitic limestone (NOT hydrated lime – calcium hydroxide!!!), will provide magnesium and calcium carbonates, as found in their their habitat, and may improve growth.

Ariocarpus, in a well draining mix, can usually be watered up to weekly in the warmth of summer. Use of a weak low-nitrogen fertilizer during the growing season can encourage growth. The main threat to their happy development is rot. Ariocarpus should be kept dry whenever there is a threat of cold. I give my Ariocarpus, which I keep in an unheated coldframe, only the smallest spritz of water occasionaly through the winter. The appearance of Ariocarpus can benefit greatly by watering the plants from the bottom. Potted plants should be stood in a pan of water until the soil has become sufficiently drenched. This practice requires a bit more effort but will help to keep the “wool” on the top of the plant from becoming matted or discolored. Some growers have costructed wooden frames encased with clear fiberglass or polycarbonate panels. Keeping your Ariocarpus in these boxes allows them to receive a lot of light and also provides the elevated air temperatures that may approximate their native desert conditions. Additionally, these boxes keep precipitation off ones plants during the cold of winter.

Fig. 6 Ariocarpus crest     Jerry Williams
Photo: Ross Shumway

Resources

E.F. Andersen The Cactus Family, 2001. A compendium of cacti, this book has a good section on Ariocarpus. Apparently the author, Andersen, has published several times on the genus Ariocarpus himself.

Ariocarpus - Living Rocks of Mexico, Website.
Site Editors: Geoff Bailey, John Miller.
This website has a wealth of information and photographs of Ariocarpus.
http://www.living-rocks.com/

CSSA Journal Vol 71 No. 4   Special Ariocarpus Issue
This issue contains several interesting and useful articles related to Ariocarpus.