Gymnocalycium saglionis aka Giant Chin Cactus

Gymnocalycium saglionis, the giant chin cactus, comes from northwestern Argentina. It belongs to the cactus family, Cactaceae. Its range includes Jujuy, Salta, Tucumán, Catamarca, La Rioja and San Juan. Wild plants grow on rocky hills in monte and chaco habitats. LLIFLE reports many plants across this range, including several protected areas. It lists no major threats to the species.

This cactus grows as a single, broad, rounded stem. Its shape can shift from a flattened ball to a short column. The stem has a dull green or blue-green surface. Garden size reports differ. RHS gives a height of 0.33 feet [0.1 metres]. It lists a spread of 0.33–1.64 feet [0.1–0.5 metres]. LLIFLE gives heights of 0.49–0.98 feet [0.15–0.3 metres]. Its largest reported plants reach 2.95 feet [0.9 metres]. RHS gives five to ten years to reach full size.

The stem has 10–32 broad ribs with low, rounded tubercles. Wavy grooves divide these ribs. Young areoles have a felt-like coat. Each bears a cluster of thick spines. Their colours range from yellow-brown through red to black. The spines turn grey as they age. Some stand almost straight; others bend outward or toward the stem. The stem's top lacks spines. Flowers form a ring near this top, among the dense spines. They have broad funnels, short tubes and white or pale pink petals. Their throats can show red. RHS places flowering in early summer. LLIFLE also reports repeat blooms through the growing season. The round fruit turns red.

RHS recommends growing this cactus under glass with good air flow. Use standard cactus compost that drains well. Its soil listing includes loam and sand, across all pH groups. Give it bright light filtered through glass. Water well during spring and summer, then keep it dry through winter. Apply a low-nitrogen liquid feed each month during active growth. RHS rates it H2: it tolerates cool conditions but not freezing.

Its ribbed stem and stout spines suit pots and patio displays. RHS lists no need for pruning. Start seeds in early spring at 19–24°C, or remove offsets in spring. Mealybugs may attack it, though RHS reports few disease problems. The supplied sources do not establish whether any parts are edible. They also provide no firm evidence about toxicity.