Mammillaria nejapensis Silver Arrows - Cactus

Sold under the name of Mammillaria nejapensis ‘Silver Arrows’, this indoor cactus is now assigned to the taxon Mammillaria karwinskiana. It is liked for its small body covered with long prickles that become silvery with age and its decidedly desert charm. It will do well on a south or west facing windowsill, on a shelf in a very bright office, a sunny living room, or a temperate conservatory.

This Mammillaria belongs to the Cactaceae family. It is native to southwestern Mexico, more precisely the state of Oaxaca, in the region of Nejapa. There, it grows between 850 and 1,650 m altitude in dry tropical forests and xerophilous formations, often on rocky ground. The name Mammillaria nejapensis is widely used in horticulture, but it is treated as a synonym of Mammillaria karwinskiana by current major botanical databases.
The slow-growing plant forms a stem that is initially globose, then shorter and cylindrical, green to bluish-green, reaching about 15 cm in height and 5 to 7.5 cm in diameter. It is solitary at first, then may branch at the base or divide. Its small pyramidal growths, arranged in a spiral, have tufts of white wool and long bristles at the base. The spines are initially cream to reddish-brown, then take on a very elegant silvery-white hue; they are straight to slightly curved and can measure up to 5 cm. The small, funnel-shaped flowers open in a crown near the apex, from spring to early summer; they are white to cream-white, crossed by a reddish vein. The elongated, red fruits do not often form indoors. 

Indoors, this Mammillaria requires very bright light with direct sun, a dry atmosphere, around 30 to 50% humidity, and temperatures of 18 to 30 °C during the growing season, with a dry winter rest period around 8 to 12 °C. It is achievable for a reasonably meticulous cactus enthusiast, the main problems coming from a lack of light and excess water in winter. Place it near a south or south-west facing window, in a bright conservatory or a well-ventilated greenhouse.

This Mammillaria will benefit from a stay outdoors from spring to autumn, exposed to the sun but sheltered from excessive rain. Bring it in before the first frosts to overwinter it in a bright, dry, and cool place, frost-free.

This variety is sought after by Mammillaria collectors. To accompany it, choose plants that love sun and a dry atmosphere: Haworthia limifolia for its raised rosette, Gasteria ‘D. Delta’ for its white-dotted leaves, Ceropegia woodii for its trailing foliage and Senecio herreianus ‘Purple Flush’ for its purplish garlands.