Darwin Was Right: The Alpine Flower *Saxifraga candelabrum* Is a Carnivorous Plant That Digests Insects

The researchers focused on S. candelabrum, a close relative of the species Darwin originally examined, which grows at altitudes of 2,500 to 3,300 meters on the Qinghai-Tibet Plateau and Hengduan Mountains in China's Yunnan and Sichuan provinces . Field surveys found insects trapped on the sticky glandular hairs of 43 out of 45 specimens examined . Mature plants snared an average of 71 insects each .

The Trapping Mechanism: A Flypaper-Style Trap

S. candelabrum’s stems and branches are covered with glandular trichomes—microscopic, hair-like structures that secrete a sticky mucilage . This creates an effective flypaper trap for small insects, primarily nonbiting midges (small flies in the order Diptera) . The plant also lures prey with scent, attracting insects to the sticky surfaces before they become ensnared .

Digestion and Nutrient Absorption: Confirmed by Modern Techniques

Once prey is trapped, S. candelabrum secretes digestive enzymes, including proteases (specifically, phosphatase enzymes), that break down the insect’s body . The researchers used a fluorescence-based assay to detect phosphatase activity on the glandular hairs, confirming the plant’s ability to digest its catch .

To prove nutrient absorption, the team conducted stable isotope feeding experiments. They fed Drosophila fruit flies labeled with nitrogen-15 (¹⁵N) to the plant and then measured nitrogen levels in plant tissues. “The authors observed a notable rise in labeled nitrogen levels in the plant’s tissues,” confirming that the plant absorbed nitrogen from its prey . The same enrichment did not occur in non-carnivorous control plants .

Transcriptome and genomic analysis further confirmed carnivory. The researchers assembled a chromosome-level genome of S. candelabrum and compared it with known carnivorous plants like the sundew (Drosera) and pitcher plant (Nepenthes). They found that genes encoding digestive protease enzymes were actively expressed in the glandular trichomes, proving the plant possesses the full genetic machinery for carnivory .

How the Plant Spares Its Pollinators

Carnivorous plants face an inherent conflict: they need to trap insects for nutrients, but they also rely on insect pollinators to reproduce. S. candelabrum solves this dilemma through clever spatial and visual separation .

The plant’s white flowers are held above the sticky stems on tall stalks, creating a physical barrier between the trap zone and the flower zone . The sticky glandular hairs are located exclusively on the vegetative stems, not on the flowers or flower stalks . This visual separation—white flowers above, sticky stems below—helps ensure that visiting pollinators are not ensnared .

This design is consistent with research on other carnivorous plants, such as sundews, where white flower color and spatial separation between flowers and traps help reduce pollinator entrapment .

Broader Implications: Many ‘Sticky’ Plants May Be Secret Carnivores

The discovery of carnivory in S. candelabrum carries profound implications for botany. This plant represents a new, independently evolved carnivorous lineage—the first confirmed carnivorous plant in the entire botanical order Saxifragales and the family Saxifragaceae .

But the researchers argue that this is likely just the tip of the iceberg. “Our findings suggest that many other plant species with sticky glandular hairs, previously dismissed as simply adhesive or protective, could be undetected carnivores,” the authors state . They note that the true number of carnivorous plant species may be substantially underestimated . “This tells us that there may be unrecognized carnivorous plants or plants with partial carnivorous characteristics in nature,” the team explained .

Key Takeaways

• Darwin proposed the hypothesis in 1875; it took 151 years for definitive proof .
• Saxifraga candelabrum is the first confirmed carnivorous plant in the Saxifragaceae family .
• The plant uses a flypaper trap of sticky glandular hairs to capture small insects .
• Modern techniques—stable isotope (¹⁵N) feeding, fluorescence enzyme assays, and transcriptomic/genomic analysis—confirmed digestion and nutrient absorption .
• Spatial separation between flowers and sticky stems protects pollinators .
• The finding suggests many other “sticky” plants may be undetected carnivores .