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Frailea amerhauseri

Amerhauser's Frailea

Overview

Frailea amerhauseri is an extremely small, solitary-growing miniature succulent subshrub belonging to the family Cactaceae. Like most members of the genus Frailea, it is highly prized by collectors for its tiny size and fascinating cleistogamous (self-pollinating without opening) flowering behavior 1.

Taxonomy and Naming

Named in honor of the prominent Austrian cactus expert Helmut Amerhauser, this species was formally described in the early 2000s. It shares close morphological affinities with Frailea castanea and Frailea cataphracta 2.

Distribution and Habitat

Native to southern South America, specifically in the Santa Cruz department of Bolivia, this cactus thrives in seasonally dry tropical biomes. It is usually found growing in gravelly soils, rocky outcrops, or tucked under the shade of small shrubs and grasses where it remains partially subterranean during dry periods 1.

Appearance

The stem is globose to depressed-globose, rarely exceeding 3-4 cm in diameter, with a dark green, grayish-green, or brownish-purple hue. Ribs are low and flattened, bearing tiny areoles with short, appressed, non-pungent spines. The yellow flowers are relatively large compared to the body but open only in extremely hot, sunny weather; otherwise, they produce viable seeds cleistogamously.

Cultivation

In cultivation, it requires shallow pots to accommodate its fibrous root system and an extremely porous, mineral-based substrate. Water moderately during the warm growing season, allowing the medium to dry out completely, and keep absolutely dry and cool during winter dormancy 2.

Common Cultivation Mistakes

Using standard, peat-heavy potting soils and overwatering are the leading causes of rot. Insufficient sun will cause etiolation and prevent the formation of buds.

Bibliography

References

  1. Plants of the World Online (POWO) - Kew Science, Frailea amerhauseri Taxon Profile. ↩
  2. GBIF (Global Biodiversity Information Facility), Frailea amerhauseri Species Records. ↩
Light

Filtered Sun

Bright filtered sun or partial shade; protect from scorching midday sun.

Watering

7-25 Days

Water dry soil in summer; keep completely dry during winter dormancy.

Soil

Highly gritty, mineral-rich soil mix with abundant pumice and coarse sand

Extremely well-draining mineral mix with high pumice and sand content.

Safety

Pet Friendly

Non-toxic and has soft, harmless spines, making it pet-friendly.

Difficulty

Moderate

Moderate; requires strict discipline with watering to prevent rot.

Native Habitat

Bolivia, South America

Native to the Santa Cruz region of Bolivia, living in seasonally dry tropical zones under sparse vegetation and nestled within fine gravelly soil.

Frequently Asked Questions

How big does Frailea amerhauseri grow?
This cactus is an extreme miniature. The stem diameter rarely exceeds 3 to 4 centimeters, keeping a very low profile.
Why does it produce seeds without the flowers ever opening?
Frailea species are cleistogamous. The flowers only open under very hot and sunny conditions; otherwise, they self-pollinate while closed and directly develop seed pods.
Is it toxic to pets?
No, Frailea amerhauseri is non-toxic. Its spines are also soft and harmless, making it very safe for homes with pets.
How often should it be watered?
In summer, water about a week after the soil has completely dried out. In winter, during its cold dormancy (November to March), keep it completely dry.
What soil mix does it prefer?
It prefers a mineral-rich, low-organic substrate composed of 50% or more pumice, lava rock, coarse sand, and a tiny fraction of loamy soil.
Should Frailea amerhauseri receive direct sunlight?
It prefers bright, filtered light or partial shade. Intense, direct summer afternoon sun can cause permanent scorching or discoloration.
What is its cold hardiness in winter?
If kept completely dry, it can survive short drops down to 5°C. The ideal overwintering temperature is between 8°C and 12°C.
Is it easy to grow from seed?
Yes, its freshly harvested seeds have a very high germination rate. However, they lose viability quickly, so they should be sown fresh.
Why is the stem shrinking and pulling into the soil?
This is a natural defense mechanism during drought or winter dormancy. The plant dehydrates to retract into the ground and will plump up again when watered.
When should it be repotted?
Due to its slow growth, repot every 2-3 years in spring, upgrading to a slightly larger pot or keeping the same size with fresh, gritty soil.