Astrophytum - Ornatum v. Mirbelii

Astrophytum ornatum var. mirbelii
Common Name: Bishop’s Cap Cactus (Mirbelii Form)

Astrophytum ornatum var. mirbelii is a standout among the Astrophytum genus, prized for its bold spines and distinctive white-flecked patterning. This variety features prominent vertical ribs lined with golden to brown spines and a dusting of silvery trichomes that create a star-like, frosted appearance. As it matures, it grows tall and columnar—making it one of the largest and most impressive species in the genus.

The mirbelii form is known for having slightly shorter spines, more defined wooly flecking, and a more symmetrical rib structure than the standard ornatum. It’s a showpiece cactus that commands attention while still offering that unmistakable Astrophytum elegance.

☀ Light Requirements
Loves bright light to full sun. Outdoors, provide morning sun and some afternoon shade in extreme heat. Indoors, place near a south- or west-facing window for strong light exposure.

💧 Watering Needs
Water thoroughly only when soil is completely dry. Highly drought-tolerant—be extra cautious of overwatering, especially in cool seasons. Reduce watering in winter.

🌡 Temperature Tolerance
Hardy down to about 25–30°F in dry conditions. Protect from prolonged frost. For colder climates or winter shipping, consider adding a [Heat Pack].

✨ Special Features
• Frosted Ribs – White trichomes create a powder-dusted, starry effect
• Architectural Shape – Grows columnar with bold, upright ribs and strong symmetry
• Rare Form – The mirbelii variety is a more refined and collectible version of A. ornatum

Other Common Names:
Mirbel’s Bishop Cap, Star Cactus (Ornatum), Frosted Monk’s Cap

This cactus will ship bare root and will be ready to place directly in a well draining soil mix like our Custom Cactus Mix.

Photos in the listings unless otherwise specified are representative of the plant that will be sent to you.
However, Plants grow differently and each plant may vary slightly in shape, size, growth pattern, etc.
Of course, if you receive a plant that you are dissatisfied with please reach out to us. We want to make it right!

If temperatures near you are below 45℉ we highly recommend adding a Heat Pack to your order.
If temperatures where you live will be much lower than 20℉ even heat packs may not work. You may consider waiting until things warm up a bit. We know you love your plants just like we do and we wouldn't want any of them to freeze.