🌱 Morphology
Solitary cactus, with a globose to slightly elongated body, 7–10 cm in diameter, with a very dark green epidermis, a characteristic that gives rise to the epithet atroviridis ("dark green"). It features 13–16 ribs about 7.5–10 mm high, slightly tuberculate. The areoles are spaced approximately 15–20 mm apart. The spination is blackish-gray and curved, with 1–5 central spines 3–5 cm long and up to 10 radial spines 2–4 cm long. It develops a hard and robust taproot.

🌍 Distribution, habitat and family
It is endemic to the Huasco River valley, in the Atacama Region, Chile, with populations in the vicinity of Vallenar and both north and south of the Huasco River. It inhabits extremely arid slopes, where it grows in stony terrain and can remain partially protected at ground level. The influence of coastal fogs helps to soften the conditions of extreme aridity. It belongs to the Cactaceae family.

According to the classification by Joël Lodé, the correct name is Guerreroa atroviridis (F.Ritter) Lodé, published in 2024. It has previously been known as Pyrrhocactus atroviridis, Horridocactus atroviridis, Neoporteria atroviridis and, subsequently, Eriosyce atroviridis.

❄️ Temperature — USDA Zone 8b–11b
It comes from an arid environment with a highly contrasting climate and can be grown with cold, dry winters. Once well-acclimated, it can withstand minimums near −7 °C during dormancy, provided the substrate remains completely dry. Cold accompanied by moisture should be avoided.

☀️ Lighting
During active growth, it needs very high lighting, approximately 18–25 mol·m⁻²·day⁻¹ of DLI PAR, with several hours of direct sun. Intense radiation favors a compact habit, the dark green coloration of the epidermis, and strong spination. During episodes of extreme heat, it can benefit from light protection during the central hours, without excessively reducing ventilation.

💧 Growth cycle and watering
It is a xerophyte adapted to extremely dry environments. During the active growth period, it is recommended to water abundantly and allow the substrate to dry completely before watering again. During winter, it should be kept practically dry, especially at low temperatures. The robust taproot allows it to have water reserves during prolonged periods of drought.

🌸 Flowering
The flowers appear near the apex and reach approximately 3.5 cm in length. They are whitish to yellow-reddish, with a reddish central line; the floral tube has small fascicles of white wool and some upward-pointing bristles. The fruit is oval, with relatively thin walls and turns red when ripe. In cultivation in Spain, flowering is expected mainly during spring.

🌿 Nutrition
During the active growth period, a fertilizer with a high content of assimilable calcium and low levels of nitrogen is recommended, such as Desert CHOICE® Cactáceas, 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 high-tech square pot and with the substrate activated with mycorrhizal fungi and biofungicides.

9x9 cm gourmet black pot