Tephrocactus alexanderi (Britton & Rose) Backeb.

🌱 Morphology

A cactus that forms loosely branched clumps, up to about 50 cm in height and width, although it usually reaches smaller dimensions in cultivation. Its numerous globose segments, approximately 3–5 cm in diameter, feature marked tubercles and an olive-green or ash-gray epidermis. They are fragile and detach easily. The areoles can produce straight or slightly curved spines, white, gray, or bluish in color, accompanied by fine glochids in pinkish or yellowish tones.

🌍 Distribution, habitat and family

It is endemic to Argentina, where it inhabits arid zones of the northwestern and west-central provinces, in sandy, stony, and occasionally somewhat saline soils. It grows in open landscapes, with high sun exposure and scarce rainfall. Joël Lodé's taxonomy maintains Tephrocactus alexanderi as a species; historical names such as Opuntia alexanderi and Tephrocactus alexanderi var. bruchii are considered synonyms or forms included within it.

Family: Cactaceae · Subfamily: Opuntioideae · Tribe: Tephrocacteae.

❄️ Temperature · USDA Zone 8b

It tolerates minimum temperatures of down to −7 °C if kept dry and well-acclimated. In cultivation, it is preferable to protect it from prolonged frosts and, especially, from the combination of cold and moisture in the substrate.

☀️ Lighting

It requires very intense lighting and can adapt to direct sun if acclimated gradually. Good exposure encourages compact growth and well-developed spination. As a guideline, a DLI PAR of 18–25 mol·m⁻²·day⁻¹ is recommended, adjusting it to growing conditions and the plant's response.

💧 Growth cycle and irrigation

Growth occurs mainly during the warm season. It is recommended to water deeply and allow the substrate to dry out completely before watering again. The substrate must be very well-draining and not retain moisture around the roots.

Winter rest. Reduce watering drastically and keep the plant dry during cold periods. In a cool winter, the dry rest helps prevent rot of the roots and segments.

🌸 Flowering

It produces large flowers, up to about 5–7 cm in diameter, which can be white, pink, or bicolored. Flowering usually takes place in the warm season, and the flowers open during the day. The age of onset and floral abundance depend on the specimen's maturity, light intensity, and management of the winter rest.

🌿 Nutrition

During active growth, Desert CHOICE® Cactáceas NPK (Ca-Mg) 4-4-7 (4-4) is recommended. Assimilable calcium promotes the formation of firm tissues and the maintenance of turgor, while magnesium participates in chlorophyll synthesis.

This is an inimitable xerophyte grown in Madrid in a technological square pot, with the substrate activated with mycorrhizal fungi and biofungicides.

◼️ Xerophyte in a 9x9 cm black pot