Acanthocalycium ferrarii Rausch · 

🌱 Morphology
 Solitary cactus, relatively fast-growing for an Acanthocalycium, with a globose or slightly depressed stem, green to grayish-green, up to about 12 cm in diameter. It has up to 18 ribs that are rounded and slightly swollen around the areoles. The areoles are oval and whitish. It develops 1–4 thick, subulate central spines, up to 1.5 cm long, and 7–9 radial spines up to 2 cm long, generally straight, horn-colored to brown, often with a darker tip.

🌍 Distribution, habitat, and family
Endemic to the northwest of Tucumán, Argentina, especially in the Sierra de Quilmes and the area surrounding Amaicha del Valle and Quilmes. It grows in xerophilous scrub and prepuna, on rocky terrain, at an altitude of approximately 2000 to 3500 m. It belongs to the Cactaceae family. Joël Lodé maintains Acanthocalycium ferrarii as the correct species; A. thionanthum subsp. ferrarii and A. thionanthum var. ferrarii remain as subordinate names/synonyms.

❄️ Temperature · USDA Zone 8b
Tolerates minimum temperatures of down to −7 ºC when kept dry and with well-acclimated specimens. Its mountain origin allows it to withstand intense cold, but the substrate must remain completely dry during periods of low temperatures.

☀️ Lighting
It requires very intense lighting and several hours of direct sun to maintain compact growth and robust spination. A DLI PAR of 20–30 mol·m⁻²·day⁻¹ is recommended during active growth, with progressive acclimation to the sun.

💧 Growth cycle and watering
Winter rest. During winter, keep it dry and protected from persistent humidity. In spring and summer, resume watering—generously but spaced out—allowing the substrate to dry completely before the next watering. In its habitat, it experiences dry periods, making it especially important to avoid waterlogging.

🌸 Flowering
It produces large flowers, up to about 5.5 cm long and 5 cm in diameter, which can vary significantly in color: yellow, orange, orange-red, and even carmine. The floral tube is provided with scales and spiny structures, a characteristic related to the name Acanthocalycium, "spiny calyx."

🌿 Nutrition
During the active growth period, a fertilizer with high assimilable calcium content and low nitrogen levels, such as Desert CHOICE® Cactáceas, is recommended, applied once a month when watering. Before flowering, it can be supplemented with Desert CHOICE® Floración.

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

9x9 cm pot