Charles Darwin loved a deep dive. The famed evolutionary biologist devoted years to studying barnacles and obsessed over breeding pigeons.
But one of his most enduring fascinations was carnivorous plants. He called Venus flytraps “one of the most wonderful plants in the world” and once remarked that he cared more about sundews, plants that sport sticky, flypaper-like traps, “than the origin of all the species in the world.”
In 1875, Darwin published a treatise on carnivorous plants that featured several species he thought could be flesh-eating flora. Among them were hardy alpine plants in the genus Saxifraga that had sticky hairs reminiscent of his beloved sundews. Darwin tempted two European Saxifraga species with insects during feeding experiments, but he was ultimately unable to prove that the species were carnivorous.
More than 150 years later, scientists have vindicated Darwin’s hypothesis. A team of researchers recently served tiny flies to another Saxifraga species native to China. Their findings, published on Tuesday in the journal Nature Communications, revealed that the plant does digest and absorb sustenance from trapped prey, expanding evidence of carnivory to a new family of plants.
According to Hang Sun, a researcher at the Kunming Institute of Botany at the Chinese Academy of Sciences and one of the authors of the paper, the findings reveal that carnivory has deep roots. “This implies carnivorous plants could be more widespread than we currently know and that more species are hiding the ability to digest prey,” he said.
Carnivory has independently evolved in 14 families of flowering plants and is defined by the trapping and digesting of prey for nourishment. Being a meat eater allows a plant to live in depleted soils and harsh habitats. Two of the most famous examples, Venus flytraps and liquid-filled pitcher plants, reside in swampy environments like bogs.
Rugged mountaintops are other places where plants struggle to cobble together nutrients from bare soil, and that’s where you’ll find Saxifraga candelabrum, a branching perennial that produces two-toned yellow flowers and grows in rock crevices in the Tibetan Plateau. Its stem and branches are covered in reddish glandular hairs that secrete a sticky substance.
During field work on a mountain in the Yunnan Province in southwestern China, Dr. Sun and his team noticed that many S. candelabrum specimens were covered in insects. During one trip, the researchers counted that mature plants, on average, had more than 70 insects stuck to their tiny hairs. The researchers wondered if the plants had evolved to catch and consume the insects.
Proving that a plant is carnivorous, however, is no easy feat. To give that label, the scientists would have to show that the species traps, digests and absorbs its prey.
First they used mesh and glass enclosures to conclude that the plant attracts insects with an odor wafting off its flowers. The plant was picky about which insects it ensnared. The glandular hairs nabbed only small insects like gnats; the larger flies that pollinate its blossoms were rarely caught. “The plant only targets small insects and keeps large pollinators safe,” Dr. Sun said.
The scientists then coated S. candelabrum with a chemical that fluoresces green if a digestive enzyme is present. The plant’s hairs did glow, confirming that active digestion was taking place.
Lastly, to investigate if the species got a meal out of the bugs, the team tracked whether the plants incorporated a nitrogen isotope from the flies placed on their hairy stems. It took S. candelabrum around two weeks to digest the flies. Afterward, the researchers collected tissue and saw the nitrogen isotope in the samples — proof that S. candelabrum absorbed nutrients from its prey.
S. candelabrum is the first confirmed carnivore in the family Saxifragaceae. But the plant is far from unique. Kadeem Gilbert, a botanist at Michigan State University who was not involved in the research, thinks there are hundreds, even thousands, of other species with similarly sticky hairs — including species like the common tomato. Many of these may also be concealed carnivores.
“This truly shows just how possible it is for carnivory to originate at any point in the plant tree of life,” he said of the new research.
Darwin would have been thrilled to probe this expanding bouquet of ferocious flora.
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