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Along with other articles, columns and club updates, each monthly issue of the Henry Shaw Cactus Digest includes an article or two on members' favorite cactus and succulent species. The articles typically include photos and facts on the plants' natural origins and distribution, growing conditions, common and scientific names, care and cultivation tips, and helpful hints for encouraging flower production.
Follow the links below this month's offering(s) to enjoy previous Plants of the Month or click to read a sample of the HSCSS Digest in PDF format.
June 2018 -- Mammillaria perezdelarosae subsp. andersoniana
By Pat Mahon
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?
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 --
International Plant Names Index -- http://www.ipni.org
June 2018 -- Trochomeria
By Bob Williams
The next group of plants on my caudiciform journey is from the Cucurbitaceae family. This is a very large family. Depending on the source, there are from 90 to 125 genera, with a total of 700 to 850 species.
Cucurbitaceae is also called the gourd family. Squash, gourds, cucumbers and watermelon are some of the fruits from plants found in this family. Plants in this family have been cultivated as a food source for thousands of years and in all parts of the world.
A few genera within Cucurbitaceae are of interest to the succulent and fat plant growers among us. Cephalopentandra, Coccinia, Coniandra, Ibervillea, Momordica and Odosicyos are a few. To see a more comprehensive list, visit the LLIFLE Encyclopedia of Succulents at https://www.llifle.com/Encyclopedia/SUCCULENTS/.
These plants produce some interesting caudices and may be of interest to members of our group. One genus you will not see is Trochomera! I don't know why. I can tell you this: there is very little literature on growing Cucurbitaceae succulents. One of the most comprehensive articles I found was written in 2001 for the Central Arizona Cactus and Succulent Society newsletter as a "plant of the month" -- http://centralarizonacactus.org/assets/newsletter/2001/CACSS_Newsletter_Central_Spine_2001_06_June.pdf.
Trochomeria was a late choice in my grand experiment. I was searching images of caudex plants, and one image called my name. The caudex was gnarly and twisted, like this author. Trochomeria debilis was the plant, and as luck would have it, Grigsby Cactus Gardens has a supply for sale.
There are nine recognized species in Trochomeria. All are found in Africa. None of the species has a very large range. T. debilis is found in Botswana and a small area of South Africa. It was first described by George Bentham and Joseph Dalton Hooker in 1867. It must not have made a very good impression, because "debilis" is derived from the Greek meaning weak, frail and feeble.
The caudex of T. debilis will grow up to 10 inches in diameter. In the wild, the caudex is completely underground, where it serves as water storage. During the growing season, the plant grows very long vines that can reach 10 feet in length. When growing T. debilis in your collection, a trellis may be needed. I would imagine the vines are not very sturdy due to the name of the plant. The plants produce both male and female flowers. The fruits are small and orange-red in color.
From what little I found about growing succulent Cucurbitaceae, it doesn't seem hard. Propagation is almost always from seed. One site said, "If you can grow zucchini, you can grow succulent Cucurbitaceae." We will have to see about that.
As with any caudex succulent, T. debilis should be grown in a well-draining soil mix. Water when the soil starts to dry in the summer and cut way back in the winter. The plants tend to be slow growers. Raising a plant with a 10-inch caudex will take time.
Periodic fertilizing during the growing season will help. Some sites say these plants do better in filtered sunlight rather than direct sun. They can withstand high temperatures. During winter months, they can take temperatures in the low 40s, but not much lower.
One thing you need to worry about is insect damage. Squash vine borers, squash bugs and cucumber beetles can be very big problems. All of the literature on insect damage is about control and vegetable crops, but I am sure the problem is the same for the plants we grow.
These pests lay their eggs in the soil in late fall, and their larvae attack plant roots during the winter. A good systemic insecticide is recommended. Pam Schnebelen told me she has information about these pests and will most likely expand on what little I wrote here.
When looking for information, I stumbled on a most interesting website, The Biodiversity Heritage Library -- https://www.biodiversitylibrary.org. The website says the library is "a consortium of natural history and botanical libraries that cooperate to digitize the legacy literature of biodiversity held in their collections and to make that literature available for open access and responsible use as a part of a global 'biodiversity commons.'"
The BHL consortium works with the international taxonomic community, rights holders and other interested parties to ensure this biodiversity heritage is available to a global audience through open-access principles. BHL has digitized over 120,000 titles and 200,000 volumes.
You can search by plant name, and the system returns results listing all printed references to that plant that have been digitized. Much of the literature dates back to the late 1800s. You can read what the early botanists wrote here. The Missouri Botanical Garden is a member of this library.
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