Echinopsis subdenudata
Synonym: Echinopsis denudata
Family: Cactaceae​
​Common Name: sea urchin cactus
Origin: Echinopsis subdenudata originates from Bolivia, South America – specifically Santa Cruz, Tarija, Chuquisaca, and perhaps Paraguay. The natural habitat includes grasslands, shrublands, and forests, 600-1,800 meters above sea level.
Description: The sea urchin cactus is a small green plant that resembles a sea urchin. Often, cacti are globular but become columnar as they age. Tiny spines are hidden within white felt areoles along 8-12 ribs, and may become larger in older cacti. In summer, funnel-shaped white flowers form at the end of long tubes, night-blooming and fragrant.
  • Interesting Features:
    • E. subdenudata is considered a race of Echinopsis ancistrophora, which is often recognized as the accepted name. E. subdenudata is separated due to its much shorter spines, often covered entirely by the felt of the areoles.
    • The flowers usually only bloom for one or two nights, wilting immediately the next day.
  • Uses: E. subdenudata is used in cultivation as a centerpiece in xeriscape gardens, especially when flowering.

Cultivation and Care:
  • Watering: Low
    • Provide monthly or weekly irrigation in summer, watering whenever soil becomes dry. The cacti will shrivel when thirsty, and plump after irrigation.
    • In the winter suspend watering – only misting occasionally.
  • Soil: Plant in light, porous soil that is well draining, and possesses a pH between 5.0-7.0.
  • Lighting: E. subdenudata prefers full sun, with partial shade on hot summer afternoons. However, do not immediately introduce to direct sunlight, as the species is easily sunburned.
  • Propagation: The sea urchin cactus can be propagated from seed, woody stem cuttings, or by offsets. Pups will develop naturally from mature cacti, and can be removed to develop a new plant. For cuttings, allow the end to callous before planting directly in soil.
  • Cold Tolerance: 20°F, USDA Hardiness zones 9a to 11b.
  • Special Accommodations: To induce flowering, move E. subdenudata to a colder (50-60°F) location during the winter, and do not water. Only somewhat frost hardy and should not be planted in very cold locations, especially if exposed to moisture.

Sources:​
  1. Llifle Encyclopedia of Cacti
  2. Cactus Art Nursery
  3. Garden Tags
  4. Garden Experiments
  5. House Plant Central
  6. World of Succulents