Named after the Belgian nurseryman De Herdt, Mammillaria deherdtiana was first described in 1969. It grows in the Mexican state of Oaxaca in barren rocky soil.
In cultivation it is not the easiest plant to grow and to keep for any length of time. M. deherdtiana requires a very gritty compost, typically 1 part John Innes to 2 parts of coarse grit; water sparingly only during the growing season. Whilst it tends to remain solitary in habitat, it will eventually form a small clump of heads each about 5cm in diameter in cultivation. The reward for successful growing is the spectacular flower, also up to 5cm in diameter, and much showier than those of many other Mammillarias which have small, almost insignificant, flowers.
There is also a subspecies, Mammillaria deherdtiana subsp. dodsonii, which was originally described as M. dodsonii in 1970, which also comes from Oaxaca. This plant was named in honour of Jay Dodson, an American accountant and succulent enthusiast who founded the International Succulent Institute (now known as International Succulent Introductions, ISI). This subspecies, unlike the type, does form small clumps in habitat, and is also somewhat easier to grow in culture. It superficially looks similar to the type, but tends to have fewer radial spines, and a slightly smaller and sometimes plainer flower.
Mammillaria enthusiasts will want to grow both plants, for the added challenge, and to be able to contrast their similarities and differences. With time, they will not be disappointed!
Tony Roberts
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