Mammillaria hahniana Werderm.
Birthday Cake Cactus, Old Lady Cactus, Old Lady of Mexico, Old Lady Pincushion, Old Woman Cactus
Mammillaria hahniana subsp. hahniana, Mammillaria hahniana subsp. werdermanniana, Mammillaria hahniana var. werdermanniana, Mammillaria saetigera, Mammillaria saetigera var. quadricentralis, Mammillaria woodsii, Neomammillaria bravae, Neomammillaria hahniana, Neomammillaria hahniana var. werdermanniana, Neomammillaria saetigera
This species is native to central Mexico (San Luis Potosí, Guanajuato, and Queretaro). It occurs at elevations from 2,460 to 7.220 feet (750 to 2,200 m).
Mammillaria hahniana is a small cactus with spherical stems densely covered with soft white hairs and white spines. The stems grow up to 3.6 inches (9 cm) tall and up to 4 inches (10 cm) in diameter, solitary or in clusters. Tubercles are short and conical. Each areole bears 20 to 30 white radial spines and 1 to 4 white central spines with a reddish tip. The radial spines are bristle-like and up to 0.6 inches (1.5 cm) long. Central spines are up to 0.2 inches (0.5 cm) long. Flowers are dark pink to reddish-purple and appear in late winter and spring, sometimes forming a ring around the apex of the stems. They are funnel-shaped, up to 0.4 inches (1 cm) long, and up to 0.6 inches (1.5 cm) in diameter. Fruits are red, club-shaped, up to 0.3 inches (0.7 cm) long, and contain tiny brown seeds.
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, the Mammillaria feature raised tubercles, from which spines emerge. When you water, the tubercles expand to allow for increased water storage. The flowers appear from these tubercles' axils 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 fertilizer during the growing season for the best results.
Repot as needed, preferably during the warm season. To repot a cactus, ensure the soil is dry before repotting, then gently remove the pot. Next, remove the old soil from the roots, removing any rotted or dead roots.
See more at How to Grow and Care for Mammillaria.
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