Synonyms:

Mammillaria duwei is considered a synonym of Mammillaria crinita by Anderson (2001) and by Fitz Maurice (2002). Considered a provisional species by Hunt (1999) and a subspecies of Mammillaria nana by Pilbeam (1999). Anyway, not all authors agree regarding the classification of this cacti and manyn still consider M. duwei as an actual separated species. Here below are its synonyms:

M. nana subspecies duwei
M. trichacantha sp. duwei
M. duwei var. longispina

Habitat:

Mammillaria duwei is a very rare species: its area of occurrance in nature extends only for 35 square kilometers! Its native area is located in the northeast of the town of Guanajuato, in Mexico, at an altitude between 1750 and 2000 meters above the sea level. Its habitat is really peculiar: it grows in in fact on volcanic rocks in scrubs populated with arid-resistant species (mainly shrubs). The survival of this species in its natural habitat is threatened by overcollection by cacti lovers and habitat degradation. Nowadays, the total population is deemed to number around 500 individuals.

Description:

Mammillaria duwei is a tiny, solitary cacti, that might form little clusters as it ages. Its small size is one of the reasons why it is so appreciated by cacti lovers and why it is so subject to overcollection in its natural habitat. The size of its stems, in fact, is around 3.5-6 centimeters in diameter and up to 4 centimeters in height. They are globose to slightly cylindrical in shape, usually dark green and, like all Mammillaria, furrowed with numerous tubercles. In M. duwei, the tubercles are small and slightly club-shaped, 4-5 millimeters long, with some woolly hair at their axiles and the areoles lying on the top of them. Spines, as in all cacti, are arranged in some radial spines (28 to 36), very light and whitish, pointing in all direction and forming a star-shaped structure. These spines form an intricate, white net on the stem, and are actually harmless. Central spines, instead, are more evident and thick. They point outwards, have a slightly hooked point, and are yellowish in colour. At the base of these central spines, there is a bright yellow spot, that make all the arrangement of the thorns look like several, numerous flowers. The actual flowers instead sprout solitary at the top of the stems in a crown-like structure, are bright yellow and rather flashy: they are one of the reasons why this species is so sought after by cacti lovers.

Cultivation:

M. duwei is not among the easiest cacti to grow. Here below are our tips:

M. duwei needs filtered light if grown outdoors as, in its natural habitat, it grows under other bushes, and plenty of light if grown indoors. Sunburnts may occur if it’s exposed to sunlight for too long. however, intense sunlights enhances healthy flowerings.
Mammillaria duwei can resist to extremely cold temperatures if its substrate stays completely dry (down to -12ºC!). However, to stay safe, we suggest to keep it at temperatures of 8-10ºC, and to keep it away from Winter rains. Some authors suggest that plants grown outdoors resist better to winter wetness, but we actually wouldn’t risk.
Provide this plant with a good ventilation: place it exposed to air drafts. During the rest period it shouldn’t be exposed to atmospheric humidity.
Water sparingly during the growth season and be extremely careful, as this plant is very sensitive to root rot. To reduce the risk of rotting, wait always for the soil to dry up completely before every irrigation. In Winter, keep its substrate completely dry.
Mammillaria duwei requires a very well-draining substrate, but with an organic part more abundant than usual. A standard mix for cacti will do good, with some peat or humus.
During the summer, fertilize once with a product specific for cacti, rich in potassium and phosphorus and poor in nitrogen. Nitrogen makes the stem of these plants too watery and fragile and enhances the risk of rotting.
Use a clay pot to enhance drainage and repot every two-three years, as M. duwei is rather slow-growing and will stay ok in the same pot for many years.

Propagation:

La propagazione può essere effettuata sia per semina che per talea, come in tutte le Mammillarie. Questa specie, tra l’altro, si trova spesso innestata su cactus più duri. L’innesto è un altro valido metodo di propagazione. I semi devono essere posti sulla superficie di un terreno sabbioso e umido a circa 20 °C. Se scegli la semina come metodo di propagazione, ricorda che i semi germinano solitamente in 8-13 giorni a temperature di 21-27ºC. Dovrebbero essere posti in un substrato leggero e mantenuti leggermente umidi e coperti con un bicchiere fino a quando non germinano. Non esporre le giovani piante alla luce solare troppo intensa. M. duwei può essere propagato molto facilmente per talea. Quando diventa sufficientemente raggruppato (dovrai aspettare un po’ più del solito perché questa specie produca polloni, a differenza di altre Mammillarie) e gli offset raggiungono una dimensione di almeno 1/3 del fusto madre, si può iniziare a staccarli con un coltello affilato. Lascia che il taglio si asciughi per una settimana o due, finché non vedi che la ferita ha formato un callo. in una pentola piena di terriccio di cactus. Le talee impiegheranno dalle 4 alle 6 settimane per radicarsi. E’ importante creare uno strato superficiale di grana grossa e adagiare su di esso la talea: impedisce alla ferita di bagnarsi troppo e, quando si formano le radici, permette loro di penetrare nel compost sottostante.

Curiosity:

Mammillaria owes its name to its tubercles, that look like nipples. The greek word “Mammilla”, in fact, means “nipple”. Mammillaria duwei is considered a synonym of Mammillaria crinita by Anderson (2001) and by Fitz Maurice (2002). Considered a provisional species by Hunt (1999) and a subspecies of Mammillaria nana by Pilbeam (1999). Anyway, not all authors agree regarding the classification of this cacti and manyn still consider M. duwei as an actual separated species.

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