Mammillaria theresae
 

Photo and © copyright by Andrea B. (Bologna, Italy) http://www.cactusfriends.com/Andrea/index.html 
 (24 flowers in late August) grafted on short Opuntia compressa stock  
 

...summer blooms

Cryptocarpic fruit: M. theresae is one of the few species of cactus with cryptocarpic fruits. That is, the fruit and seeds are produced and retained inside the stem of the plant. After the flower is finished and dropped off, the stem closes over the fruit and the fruit/seed gradually ripens within. The following years the fruit may remain within the body at the axil, or may protrude a bit.  A thin membrane will be above the part where ripe seed can emerge. As the plant swells with the new growing season, the membrane fractures, and some seed from the past years can little by little drop down and germinate in the close proximity, forming small colonies.
But usually the seeds remain within the plant body for several years or for the whole life cycle of the plant, and frequently  they will be released only at the death of the plant after the disintegration of the old  stem.
It is possible to collect fruit and seeds only by means of a thin pointed forceps. The seeds' vitality lasts for many years and  moreover  seeds contain inhibitors that preserve them from premature germination.  Generally fresh seeds won’t germinate very well, only old seeds do. The complete germination of this kind of seed may take several years (Some will sprout unexpectedly after 5 or 8 years!). Because of the above peculiarity, seeds and plants of cryptocarpic Mammillaria (Series Longiflorae)  are seldom available from commercial sources.

Buds and flowers remnants.

Cultivation: M. theresae - like the other Mammillarias of the saboae group - is not the easiest of Mammillarias to grow and keep, this is  though it is easier than some of its relatives such as M. goldii.  But all this species require similar growing conditions, and a mineral-based potting mix is preferred. They need to be kept dry in winter.
Pot plants are quite wet-sensitive. Care must be taken with watering, and it needs good drainage.  Water sparingly during the growing season; keep very dry in winter.  But plants grown outdoors seems to tolerate easily the winter wetness.  Usually it is recommended to overwinter this plant in a bright and warm greenhouse with at least 8-10° C , but it has proved to be quite frost resistant and has demonstrated to survive safely outdoors under a cover of snow at a temperatures of -15° C.  Sun Exposure: Full sun - Light shade.

Propagation: Seeds, cuttings or grafting. Germination of the seed can still prove to be a challenge.
 

Seasonal growth and contraction:
In the wild these plants contract considerably during the dry season, sometimes pulling down completely under the soil level, and frequently the flowers push up through the dirt from the underground cactus body.  In fact, even though these plants show a good amount of new growth each year (at least two or three cm), they hardly get any larger, and their dimensions remain unvaried year after year, as the individual stems tend to contract at the base. The new growth produced during the vegetative season compacts considerably and retracts sometime,s pulling the plant down completely under the soil in the hottest months of summer and coldest months of winter.
It should be noted that "when specimens are in this withdrawn state, it becomes almost impossible to find them in their natural state, even though their exact locality is known"
See also: Dehydration/rehydration cycles

Conservation status: Listed in CITES appendix 2.
 

Synonyms: Mammillaria saboae var. theresae

Series: "Longiflorae"

M. theresae is one of a number of  similar species, all discovered in the 1960s, the others being M. saboe, M. haudeana, and M. goldii. Mammillaria theresae was first described in 1967,
 

Distribution: Endemic to the Mexican state of Durango in the Coneto Mountains, (West Sierra Madre) where it is found only at its type locality.
 

Habitat: Grows mainly in moss patches over rock formations on the eastern slopes of the Coneto Mountains, at altitudes of about 2200-2300 m. The mountainous habitat is characterized by serious temperature fluctuation.

Etymology: The genus name "Mammillaria"  is derived from the Latin word “mammilla” incorrect spelling of “mamilla”; which means “breast, teat, nipple” and refers to the small tubercles (fleshy lumps or warts) covering the plant body. All cacti in this genus are rib-less ( The genus name implies: "bearing nipples (tubercles)")
The species epithet "theresae"  has been named after Theresa Bock who, together with her husband John, discovered the plants on the Coneto Mountains in Durango, Mexico, in 1996.
 

Outdoor in a rock garden: a plant emerge from the melting snow. This mountainous species is quite frost hardy, it can withstand night temperature down to - 15° C

 The habitat at Coneto Pass (Photo by: Wolter ten Hoeve)
▲Above: In time of drought (2002)
▼Below: A clustered plant submerged by abundant rain (2003)

 

Photo of conspecific taxa, varieties, forms and cultivars of Mammillaria theresae:

• M. theresae
• M. theresae (The habitat - Coneto Pass)
• M. theresae forma brevispina
• M. theresae forma polytomica
• M. theresae forma cristata
• M. theresae forma albiflora