Mammillaria guelzowiana Werderm.
Krainzia guelzowiana, Phellosperma guelzowiana, Bartschella guelzowiana
Mammillaria guelzowiana is a small cactus with globose, apically depressed stems with conical and cylindrical tubercules tipped with areoles that bear clusters of numerous spines. The stems grow up to 2.8 inches (7 cm) tall and up to 4 inches (10 cm) in diameter, solitary at first but clustering at a very young age. Each areole bears 1 to 6 central spines, one usually hooked, and 60 to 80 radial spines. The central spines are reddish-brown to yellow and up to 1 inch (2.5 cm) long. The radial spines are white, hair-like, and up to 0.6 inches (1.5 cm) long.
The flowers are bright pink to purplish red and appear in late spring and summer. They are bell-shaped, up to 1.6 inches (4 cm) long, and 2.8 inches (7 cm) in diameter. Fruits are pale red or yellowish-white, almost globose, and up to 0.3 inches (0.8 cm) in diameter.
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 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, make sure 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 as you repot. Leave the plant dry for a week or so, then begin to water lightly to reduce the risk of root rot.
See more at How to Grow and Care for Mammillaria.
Mammillaria guelzowiana is endemic to Mexico.
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