The Puna bonnieae ‘Inermis’ (accepted scientific name - Maihueniopsis bonnieae cv. Inermis) is a rare and fascinating species of cactus that captivates enthusiasts with its compact, globular growth habit and distinctive spination—or lack thereof. Unlike the standard Puna bonnieae, which features sharp spines, the ‘Inermis’ variety is notable for being nearly spineless, making it a more approachable choice for collectors and indoor growers. This unique adaptation enhances its ornamental appeal, making it an excellent choice for rock gardens, succulent arrangements, and specialized collections. 

Puna bonnieae is native to the high-altitude regions of Argentina, particularly in the Catamarca Province. It thrives in rocky, arid landscapes where it has adapted to survive extreme temperature fluctuations. Its habitat consists of well-draining, sandy soils and a dry climate, making it exceptionally drought-tolerant. 

This slow-growing Puna cactus forms small, round segments that cluster together, creating a low-growing mound over time.

It remains compact, rarely exceeding 6 inches tall, making it ideal for container cultivation and small garden spaces.

Each segment is about 2 inches wide, with a smooth, green surface that may develop slight texture with age.

Unlike many other cacti, Puna bonnieae ‘Inermis’ has tiny, nearly invisible spines, making it safe to handle.

The flowers of this Puna bonnieae ‘Inermis’ typically bloom in spring and early summer.

The petals of a flower are a light honey-yellow when it first opens, but they darken with age.

On the second day, before they fade, the petals turn into a rich tan-rose color. Yellow and pink flowers are occasionally found together. These blooms are short-lived but attract pollinators like bees, butterflies, hummingbirds, and other beneficial insects, making them a valuable addition to a pollinator-friendly garden. 

When it comes to care, the Puna bonnieae ‘Inermis’ thrives in full sun to bright indirect light. When growing indoors, a south-facing window or a grow light will help maintain its compact shape and healthy coloration. Keep it in temperatures between 60-80°F. It prefers low humidity, making it an excellent choice for dry indoor environments. Good air circulation is recommended to prevent fungal issues. 

When grown outdoors, it should be placed in a spot where it receives at least 6-8 hours of direct sunlight per day.

It is hardy in USDA zones 8-11, tolerating temperatures down to 20°F if kept dry.

In colder zones, it should be brought indoors or protected from frost with coverings or by placing it in a greenhouse.

Like most cacti, opens in a new tab, this species prefers deep but infrequent watering. Water only when the soil is completely dry, typically every 2-3 weeks in the growing season and once a month or less in winter. Use a well-drained specialized cactus  soil  mix, opens in a new tab. 

A low-nitrogen cactus fertilizer (such as 5-10-5) can be applied once a year during the active growing season.

The Puna bonnieae ‘Inermis’ can be propagated through offset division or seeds. Offsets can be gently removed and allowed to callous for a few days before being planted in dry soil. Seeds take longer to germinate and require warm temperatures and patience. Due to its slow-growing nature, propagation success rates can vary, but offsets generally establish quicker than seeds. 

According to ASPCA, the Puna bonnieae ‘Inermis’ is not known to be toxic to pets or humans, making it a safe choice for households with animals. However, while it lacks large spines, some species in the Puna genus have small, hair-like glochids, so handling with care is still recommended.