Mammillaria karwinskiana Mart.
Royal Cross, Royal Cross Cactus
Cactus geminatus, Cactus pyrrhocephalus, Cactus subpolyedrus, Cactus virens, Mammillaria closiana, Mammillaria collinsae, Mammillaria confusa var. conzattii, Mammillaria conzattii, Mammillaria ebenacantha, Mammillaria flavescens, Mammillaria geminata, Mammillaria jalappensis, Mammillaria karwinskiana subsp. karwinskiana, Mammillaria karwinskiana var. flavescens, Mammillaria karwinskiana var. virens, Mammillaria karwinskii, Mammillaria malletiana, Mammillaria malletiana var. pyrrhocephala, Mammillaria polygona, Mammillaria pyrrhocephala, Mammillaria pyrrhocephala var. donkelaerii, Mammillaria pyrrhocephala var. malletiana, Mammillaria seitziana, Mammillaria subpolyedra, Mammillaria virens, Mammillaria voburnensis subsp. collinsae, Mammillaria voburnensis var. collinsae, Neomammillaria collinsae, Neomammillaria conzattii, Neomammillaria pyrrhocephala, Neomammillaria subpolyedra
This species is native to Guatemala and Mexico (Chiapas, Oaxaca, Puebla, Morelos, Guerrero, Michoacán, and Colima). It occurs in tropical deciduous forests and xerophilous scrub at elevations between 490 and 6,890 feet (150 and 2,100 m).
Mammillaria karwinskiana is a small cactus with green, spherical to short cylindrical stems with pyramidal, spirally arranged tubercles tipped with clusters of spines and tufts of white hair and long white bristles in axils of the tubercles. The stems grow up to 8 inches (20 cm) tall and up to 4.8 inches (12 cm) in diameter, solitary or slowly branching basally or dichotomous. They develop white tomentum at the apex. Each areole usually bears six straight to slightly curved radial spines. They are up to 1.2 inches (3 cm) long, cream to reddish with a brown tip, becoming chalky white with age. The central spines are absent. Flowers are funnel-shaped, cream to medium yellow with purplish midveins, and appear in spring, forming a circle around the stem just below the apex. They are up to 1 inch (2.5 cm) long and up to 0.6 inches (1.5 cm) in diameter. Fruits are red, club-shaped, and quite attractive.
The specific epithet "karwinskiana (kar-winz-kee-AH-na)" honors Wilhelm Friedrich Karwinsky von Karwin (1780-1855), a Bavarian naturalist who collected plants and animals in Brazil (1821–1826) and Mexico (1826–1831, 1840).
How to Grow and Care for Mammillaria karwinskiana
Light: Plant this cactus in an area of your garden that receives 4 hours of direct sunlight a day. If you are growing M. karwinskiana indoors, place it near the brightest window in your home or office to ensure your cactus gets enough light. If possible, place the pot on the balcony or in the garden for extra light from spring to fall.
Soil: M. karwinskiana requires a soil mix that provides root aeration and good drainage, whether grown outdoors or indoors. Use a commercial cactus potting mix or create your own.
Temperature: This cactus is heat tolerant, but it is not a cold-hardy plant. M. karwinskiana can withstand temperatures as low as 25 °F (-3.9 °C). USDA Plant Hardiness Zones 9b to 11b, 25 to 50 °F (-3.9 to 10 °C).
Watering: From spring to fall, water deeply and wait for the soil to dry out before watering again. Never let the pot sit in water. Suspend watering in the winter.
Fertilizing: M. karwinskiana can benefit from fertilization during the growing season. Apply a water-soluble fertilizer for cacti and other succulents. Suspend feeding during the winter when the plant goes dormant.
Repotting: Repot every two or three years into a slightly larger pot. The best time to repot your M. karwinskiana is late winter or early spring, but the repotting process can be done almost any time of the year.
Propagation: There are two easy ways to propagate M. karwinskiana: by seeds or by dividing offsets. The best time to remove offsets is in spring and summer. Sow the seeds in late spring or summer.
Learn more at How to Grow and Care for Mammillaria.
Toxicity of Mammillaria karwinskiana
M. karwinskiana is considered non-toxic to both humans and pets.
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