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Mammillaria magnimamma priessnitzii

Origin and Habitat: central
Habitat and ecology: It grows in dry rocky places in the open or (mainly) in xerophyllous vegetation. Despite the great abundance and diversity of cacti in Mexico, Mammillaria magnimamma is one of the few cacti species that has colonized barren lava fields. In parts of its range the species is threatened by local extraction for ornamental plant trade and by the expansion of urbanized areas.

Description: Mammillaria magnimamma is a perennial stem succulent solitary at first, later branching basally to form large mounds up to 50 cm in diameter . barely rising above ground level. This species is very variable and has received many names.
Flowers: Dirty white, creamy-yellow or tinged brown with reddish midveins, to deep purplish pink, 20-25 mm wide and long and in diameter.
Blooming season: Mid spring.

Cultivation and Propagation: Mammillaria magnimamma is easy to cultivate, and makes an interesting specimens. Over time it will produce large clumps. It grows by producing offsets, and also by dividing and doesn't require any special treatment, but needs as much light as possible without burning the plant, to keep the stems compact. During the summer it is best to keep the plants outside where the temperature can rise to over 30° C with no harm to the plant, recommended for any collection that needs lots of light with ample airflow.
Growth rate: It is a small growing, but easily flowering species. It takes several years to offset, but once it starts it can fill a 40 cm pot in a few years given the best conditions.
Watering: It likes a winter's rest and should be kept almost completely dry during the winter months, If the soil is allowed to be dry for too long root loss could follow but equally the same result would occur if the plants are both wet and cold. From March onwards the plant will begin to grow and watering should be increased gradually until late May when the plant should be in full growth. Water regularly during the summer so long as the plant pot is allowed to drain and not sit in a tray of water.
Hardiness: Grown specimens resist to -4°C for a short time

Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz