Study Confirms Darwin's 1875 Prediction That Saxifraga Plants Are Carnivorous

A study published August 4 in Nature Communications has confirmed a 150-year-old hypothesis by Charles Darwin that certain plants in the genus Saxifraga are carnivorous. Darwin proposed in 1875 that sticky hairs on these alpine flowers might trap insects, but his experiments were inconclusive before his death.

Researchers focused on Saxifraga candelabrum, which grows at high altitudes in China's Hengduan Mountains. Mature plants averaged 71 insects stuck to the glandular hairs on their inflorescence branches, while juvenile plants with fewer branches trapped few or none, suggesting branch density correlates with capture success.

Experiments enclosing flowering plants in glass or mesh showed the species attracts insects primarily through odor rather than visual cues. The plants selectively trap small insects while rarely catching effective pollinators, indicating a mechanism to preserve pollination relationships.

Chemical analysis revealed the plants use phosphatase, an enzyme common in other carnivorous plants, to digest captured prey. To test nutrient absorption, researchers fed the plants fruit flies labeled with a nitrogen isotope; nitrogen levels rose in S. candelabrum but not in a control plant.

Genetic analysis provided additional evidence, showing that S. candelabrum shares genes with other known carnivorous plant lineages. Study co-author Hang Sun of the Kunming Institute of Botany stated the genomic data independently confirm the species as a true carnivorous plant.

Co-author Doug Soltis of the University of Florida suggested carnivory may be more widespread in the Saxifraga family than previously recognized, as other members also possess sticky hairs. Botanist Susan Myers of the Pittsburgh Botanic Garden, who was not involved in the research, noted the findings highlight how much remains unknown about plant biology.