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Arthrocereus spinosissimus

Spiniest Joint-Cactus

Overview

Arthrocereus spinosissimus is a rare, highly spiny, and slender succulent subshrub belonging to the Cactaceae family 1. Native to the seasonally dry tropical savannas of Brazil, this species is appreciated by collectors for its fragile, jointed stems and beautiful nocturnal flowers.

Taxonomy and Naming

Belonging to the tribe Trichocereeae within the Cactaceae family, the genus name Arthrocereus is derived from the Greek word 'arthron', meaning joint, referencing the segmented look of the stems. The specific epithet spinosissimus means 'most spiny' in Latin, directly pointing to the extremely dense golden-brown spines covering the plant 2.

Distribution and Habitat

This species is endemic to central Brazil, particularly found in Goiás, Distrito Federal, Mato Grosso, and Mato Grosso do Sul 1. It thrives on rocky outcrops and sandy fields within the 'Cerrado' savanna ecosystem. Due to habitat destruction caused by agriculture, it is classified as Vulnerable (VU) by the IUCN 3.

Appearance

Arthrocereus spinosissimus forms branched, upright cylindrical stems that reach up to 3-5 cm in diameter. The stems are divided into multiple shallow ribs, which are densely packed with fine, yellowish-brown acicular spines. The long, funnelform white to cream-colored flowers open at night to attract nocturnal pollinators.

Cultivation

In cultivation, this cactus requires exceptional drainage and bright, filtered light. During the spring and summer active growth phases, it should be watered thoroughly only after the substrate has completely dried. In winter, watering should be reduced to an absolute minimum to prevent rot.

Common Cultivation Mistakes

The most frequent mistake is keeping the soil too damp or using organic-heavy soil mixes, which leads to rapid root rot. Insufficient light exposure also causes etiolation, where stems grow weak, pale, and unnaturally thin.

Bibliography

References

  1. Plants of the World Online (POWO). Royal Botanic Gardens, Kew. Kew Science. ↩
  2. Anderson, E. F. (2001). The Cactus Family. Timber Press, Portland, Oregon. ↩
  3. IUCN Red List of Threatened Species. International Union for Conservation of Nature. ↩
Light

Bright Indirect Light

Prefers bright, indirect light or filtered sun; shade causes undesirable elongated, weak growth.

Watering

10-30 Days

Water only when the substrate is fully dry; reduce watering to a minimum in winter.

Soil

Well-draining, mineral-rich cactus grit mixed with pumice and coarse sand

Requires highly porous, inorganic-heavy cactus soil mixed with plenty of pumice or grit.

Safety

Pet Friendly

Non-toxic to pets, but the extremely dense, sharp spines can cause painful skin irritation.

Difficulty

Moderate

Moderate care level; requires precise winter moisture control and excellent drainage.

Native Habitat

Brazil

Naturally distributed across the sandy, rocky slopes of the Cerrado savannas in central Brazil, adapted to dry, nutrient-poor soils.

Frequently Asked Questions

Is Arthrocereus spinosissimus toxic to pets?
No, this cactus is non-toxic. However, its dense and sharp spines pose a physical hazard to curious pets.
How often should I water this cactus?
During summer, water roughly every 10 days (only when soil is bone dry), and reduce to once a month or less in winter.
What type of soil should I use?
Use a mineral-heavy cactus mix enriched with plenty of pumice, lava rock, and coarse sand to ensure quick drainage.
Does Arthrocereus spinosissimus bloom?
Yes, mature plants produce showy, fragrant, white-to-cream funnelform flowers that open on summer nights.
Can it tolerate direct sunlight?
It can tolerate direct morning sun if acclimated, but protection from scorching midday sun is highly recommended.
What is its growth rate?
It has a slow to moderate growth rate, gradually branching from the base to form a small spiny clump under optimal care.
Where should I keep the cactus in winter?
Keep it in a bright, frost-free room with a minimum temperature of 8-10°C for a dry winter dormancy.
Why is the stem growing thin and elongated?
This is known as etiolation, a classic sign of insufficient light. Move the plant to a much brighter location.
When should I repot this cactus?
Repotting is typically done every 2-3 years in early spring, only when the root system has fully outgrown its current pot.
How do I prevent root rot?
Prevent root rot by using pots with drainage holes, avoiding standing water in the saucer, and never watering wet soil.