Mammillaria bertholdii (2019)

By Pat Mahon (February 2019)

SiPhotonce many of the larger cacti have already been discovered, there are plenty of diminutive species still hiding away. One of these happens to be a gorgeous new Mammillaria species with a growing habit simlar to that of Ariocarpus. This new species does not resemble rocks and gravel though, but instead looks like a cluster of perfect eyelashes.

A remarkable find in the cactus world, Mammillaria bertholdii was only recently discovered in 2013 by Andreas Berthold in Oaxaca, Mexico. This is one of the laughably disproportionate cacti, in which the flower and the tuberous root system are generally much larger than the entire plant!

The elevation and topography of M. bertholdii’s habitat in Oaxaca are quite variable. Much of Oaxaca is diverse, leading to a surplus of unique and endemic species. There are pine trees scattered among what seems to be the surface of the moon. The mammillarias grow in rocky shale with shallow soils mostly devoid of organic matter. Most plants grow on the tops or slopes of the barren hills.

Facing few threats in situ due to poaching, the flat geophytic habit of the plant may actually hide further distribution ranges. The area in which this species is recorded has been reduced to a mere 10 square kilometers. M. bertholdii may have a chance to avoid future human threat, just because the plants managed to evade over 300 years of detection! The Mexican government does not even know the species’ location.

To give some clarity, M. bertholdii has been classified as part of the Saboae Group, which has beauties such as M. theresae and many subspecies of M. saboae. These species are generally found in the volcanic belt in the Sonoran/Chihuahuan Desert regions of Mexico, while M. bertholdii is found further south in a diverse region in Oaxaca.

This is seen as unusual, in that there are no known transitional species for the group between those regions. In other words, there may still be undiscovered species within the group — or taxonomists have incorrectly placed M. bertholdii in the Saboae Group! An author has proposed that the plant may actually belong to an ancestral clade.

If you are lucky enough to have obtained this elusive species in the hobby, the plants’ care is fairly easy. Since M. bertholdii is almost always offered as a grafted plant, we will focus on this cultivation method.

As a grafted plant, M. bertholdii is quick to grow and divide. The plants are quite indestructible, it seems, as our grafted plant was knocked back to a couple of sad tubercles due to spider mites and came back to a full, large plant in a matter of months.

M. bertholdii grows in full sun, and is not shy to take on gratuitous amounts. Avoid full sun and extreme heat, but the pectinate eyelashlike spines do help shade the body of the plant. Remember, you are watering the bottom rootstock to sustain the top scion cactus. Identify and understand your rootstock cactus, and ensure the scion gets enough light to avoid etiolation.

Watch out for several major pests: spider mites and mealy bugs. They can quickly ravage the plant, as tubercles seem to abort to help save the plant. Quick treatment will keep the plant alive and let you come to the calm realization that the plant will continue to grow. In time, mature growth with part of the rootstock intact could be grown on its own roots. Simply place in a well-drained substrate and do not water until roots appear.

Photo If your grafted plant is not very tough, chances are its vigor is diminished due to overpropagation. Experienced in the cacti hobby and with other plant families with rarer species in high demand, the issue is that vigor is reduced when some plants have been divided, grafted, divided and grafted, again and again. If they were instead micropropagated, vigor could be maintained or even increased. Don’t feel bad if you are doing everything right, and your plant dies, because the cause may not be you!

M. bertholdii is very infrequently offered on its own roots. Plants on their own roots without definite greenhouse provenance are typically illegally pillaged plants. At all costs, do not buy these plants. Responsible seed collection by authorized personnel is the only acceptable way for these plants to enter the hobby.

In the event you had a spare $150 to buy a plant grown from seed on its own roots, your purchase should be hardy. However, M. bertholdii are seldom offered as seed-grown plants, since they are cryptocarpic – fruit and seeds are produced and retained within the plant body. The seeds have inhibitors to prevent immediate germination. The plants are reportedly sensitive to overwatering. In winter, they retract in size, so avoid watering.

Since this species is so new and its location kept secretly protected, there is little more to learn about M. bertholdii at this time. The future may hold some interspecific crosses between the Saboae Complex that verify its place in the genus. We can hope to learn of how unique regions influence endemic species, and possibly apply this assessment to predicting where other undiscovered diminutive species may lie waiting.

Llifle Encyclopedia of Cacti – 2468/Mammillaria_bertholdii
Xerophilia, March 2017 – Mammillaria bertholdii Linzen, Three Years After Its Description –