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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.
April 2018 -- Mammillaria geminispina
By Joseph Merkelbach
Mammillaria geminispina is named for the pattern of its spination -- twin-spined -- but that only refers to the central spines. There are actually sometimes up to six central spines, and also 16 to 20 radials that surround them.
All these spines are pretty stiff and white-colored, some with light-brown tips. One variety, called nobilis, has central spines up to 40 millimeters long. There is also some white wool in the axils between tubercles, particularly on the top surface.
All this bright white color is the source of a nickname, Whitey, which seems appropriate for the large and bright, mound-shaped specimens seen in shows. The cactus can take a single, globular form, but more often a grouping of globes, with the older ones in the center, eventually forming cylindric or club-shaped forms.
The flowers are about 2 millimeters long with carmine red petals that are paler at the edges. The stigmas are pinkish, ranging from red through a yellow-tinted coloration. They bloom in the typical Mammillaria ring around the top of the body, but frequently with only a few open flowers at a time, thus forming incomplete rings.
The native habitat of Mammillaria geminispina is in parts of three central Mexican states: Hidalgo, Queretaro and San Luis Potosi. The plants live in areas ranging from 1,000 to 1,850 meters in altitude.
M. geminispina is one of the oldest named species of Mammilaria. The currently accepted description and naming was by Haworth in 1824 from a specimen brought to London from Mexico.
The plant is easily cultured, requiring good drainage and plenty of sunlight in the summer to maintain maximum white growth. Winter can be very dry, but with no exposure to freezing.
Mammillaria -- John Pilbeam, Cirio Publishing Services Ltd.
Llifle Encyclopedia of Cacti -- http://www.llifle.com/Encyclopedia/CACTI/Family/Cactaceae/14012/Mammillaria_geminispina
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