Mammillaria guelzowiana Werderm.
Krainzia guelzowiana, Phellosperma guelzowiana, Bartschella guelzowiana
Mammillaria guelzowiana is a small cactus, solitary at first, but it clusters at a very young age. Stems are globose, apically depressed, with conical and cylindrical tubercules. They grow up to 2.8 inches (7 cm) tall and up to 4 inches (10 cm) in diameter. It has 1 to 6 central spines, one usually hooked. They are reddish-brown to yellow and up to 1 inch (2.5 cm) long. The 60 to 80 radial spines are white, hair-like, and up to 0.6 inches (1.5 cm) long. Flowers are bell-shaped, bright pink to purplish red, up to 1.6 inches (4 cm) long, and up to 2.8 inches (7 cm) in diameter. They appear in late spring and summer. 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 will 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, make sure the soil is dry before repotting, then gently remove the pot. Knock away the old soil from the roots, making sure to remove any rotted or dead roots in the process. Treat any cuts with a fungicide. Place the plant in its new pot and backfill 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. See more at How to Grow and Care for Mammillaria.
It is endemic to Mexico.
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