Mammillaria muehlenpfordtii C.F.Först.
Cactus muehlenpfordtii, Neomammillaria muehlenpfordtii, Mammillaria celsiana,
This species is native to Mexico. It occurs in Querétaro, Guanajuato, and San Luis Potosí at elevations between 5,580 and 7,880 feet (1,700 and 2,400 m).
Mammillaria muehlenpfordtii, formerly known as Mammillaria celsiana, is a small cactus with spherical to short cylindrical stems with conical to pyramidal tubercles, each tipped with a small woolly areole and a cluster of white and yellow spines. The stems grow up to 8 inches (20 cm) tall and up to 6 inches (15 cm) in diameter, initially solitary, later dividing dichotomously at the apex. They are dark green, blue-green, or grey-green. The apex of the stems is slightly sunken and woolly. Each areole bears 24 to 50 bristle-like, up to 0.15 inches (0.4 cm) long, white or yellowish radial spines and usually 4 stiff, up to 1.6 inches (4 cm) long, pale yellow central spines with a brown tip.
Flowers are small, shiny, carmine to rose red with reddish-brown outer petals and appear in a ring near the top of the stem in summer. Fruits are red, club-shaped, and contain tiny brown seeds.
USDA hardiness zones 9b to 11b: from 25 °F (−3.9 °C) to 50 °F (+10 °C).
How to Grow and Care
To encourage better flowering, allow the plants to enjoy a cooling period in the winter and suspend watering. Unlike many other cacti, which use their ribs as storage devices, Mammillaria feature raised tubercles, from which spines emerge. When you water, the tubercles will expand to allow increased water storage. The flowers emerge from the axils of these tubercles on the previous year's growth, which accounts for their interesting halo effect. The cactus mustn't be exposed to prolonged dampness and sitting water. Never let your cactus sit in a dish of water. Lastly, ensure to fertilize during the growing season for the best results.
Repot as needed, preferably during the warm season. To repot Mammillaria, ensure the soil is dry before repotting, then gently remove the pot. Knock away the old soil from the roots, removing any rotted or dead roots. Treat any cuts with a fungicide. Place the plant in its new pot and backfill it with potting soil, spreading the roots out as you repot. Leave the plant dry for a week or so, then begin to water lightly to reduce the risk of root rot.
Learn more at How to Grow and Care for Mammillaria.
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