– Mammillaria perezdelarosae (2018)

By Pat Mahon (June 2018)

Mammillaria gets quite a bit of attention these days – and rightfully so! The incredible arrangements of tubercles and spines of plants in this genus are among the most diverse of any genus in Cactaceae, with around 200 observed species.

The systematics of the genus Mammillaria have been seen as polyphyletic (from multiple evolutionary ancestors), while experiencing plenty of segregations into genera such as Escobaria and Coryphantha. Mammillaria is undoubtedly a genus that may eventually be intensely divided based upon molecular DNA analysis, further clouding our understanding of this incredible group of cacti. In other words, always use a pencil to write that name on your plant labels!

In the field, a plethora of new species of Mammillaria is being found. These new taxa are not some boring, ugly cacti, but unique and diminutive additions to our collections. Most are unfortunately rapidly collected and pillaged, putting them at risk.

Mammillaria perezdelarosae subsp. andersoniana could be regarded as one of the rarest and most attractive newer species in all of Mammillaria. Does this seem like a bold statement? Well, check it out!

First described by W.A. and Betty Fitz Maurice, M. perezdelarosae subsp. andersoniana was originally collected in June 1999 in the municipality of Villa Garcia, Zacatecas, Mexico, at around 2,000 meters elevation. Described as a new subspecies in 2001, this taxon has only recently been seed cultivated and offered more abundantly in cultivation.

Unfortunately for the U.S. market, the plants remain very rare. There are estimated to be less than 1,000 plants left in situ in an area of only 1,000 square meters, so this plant is considered critically endangered. Because this is a diminutive and cryptic species, these numbers may in fact be higher with wider distribution, but poaching continues to be the primary reason for decline in populations.

This year, M.A. Diaz reported overlap in distribution between M. perezdelarosae subsp. andersoniana and its ancestral M. perezdelarosae in the state of Aguascalientes, but the plants may no longer be present as a result of poaching. Leo Rodriguez recorded a 2017 occurrence in Aguascalientes near the border of Zacatecas at about 2,300 meters elevation. There is still some hope for this species evading extirpation – and possible discovery of increased distribution!

The major difference between M. perezdelarosae subsp. andersoniana and its ancestral species M. bombycina and M. perezdelarosae are the former’s straightened central spines borne upon short, solitary stems. Both ancestral species have fish hook spines, which display curved tips.

The flowers share a very similar morphology among these species, as M. perezdelarosae subsp. andersoniana produces only white-yellow flowers displaying a faint brownish midstripe. The intrigue of this species seems to be the shorter, straightened bicolored central spines, surrounded by pectinate, symmetrically arranged radial spines that number from 50 to 63 per tubercle. Tubercles are not visible, because the radial spines and small amount of adaxial wool obstruct viewing them.

This subspecies is much slower-growing than its related taxa M. perezdelarosae and M. bombycina, and is also considerably smaller in stature. It tends to have a solitary stem and rarely offshoots in cultivation. It is very sensitive to overwatering and requires a porous, neutral substrate in a shallow pot.

The plants can be momentarily frost-hardy to 23 degrees F, but require at least 41 degrees F to grow well. The mean temperatures in situ suggest this species does not grow where it is very warm, and most nighttime lows are from 32 to 52 degrees F.

M. perezdelarosae subsp. andersoniana requires higher light for proper spine development, but cannot tolerate full sun. Place it where a good amount of morning sun is given, but keep it sheltered by afternoon shade. Use a high-potassium fertilizer in summer.

M. perezdelarosae subsp. andersoniana is one of the rarest cacti that doesn’t have to be grown in full sun, requires less care, grows in lower temperatures and is acclaimed to be one of the most beautiful mammillarias out there. What more can we desire in a cactus?

Sources:
The Encyclopedia of Cacti – http://www.llifle.com/Encyclopedia/CACTI/Family/Cactaceae/11896/Mammillaria_perezdelarosae_subs._andersoniana
Wikipedia – https://en.wikipedia.org/wiki/Mammillaria
iNaturalist Observations – https://www.inaturalist.org/taxa/207303-Mammillaria-perezdelarosae-andersoniana
International Plant Names Index – http://www.ipni.org