For most insects, a flowering alpine plant might seem an unlikely predator. But researchers have discovered that a delicate wildflower that grows in rocky mountain crevices in southwestern China lures prey onto sticky hairs, digests their bodies and absorbs the nutrients left behind. It is the first confirmed carnivorous plant in its botanical grouping.
Its scientific name is Saxifraga candelabrum, and it is a member of a diverse botanical order — a taxonomic category — called Saxifragales that spans more than 2,000 species.
The plant grows on nutrient-poor rock faces in the Qinghai-Tibet Plateau and Hengduan Mountains of China, ranging from central and northern Yunnan Province to southwestern Sichuan Province at elevations of 2,500 to 3,300 meters (8,200 to 10,800 feet). It is covered with sticky reddish glandular hairs that trap small insects.
Carnivorous plants are best known from swamps and wetlands, where species such as Venus flytraps, pitcher plants and sundews supplement scarce nutrients by catching prey.
To qualify as truly carnivorous, a plant must do more than accidentally catch insects. It must absorb nutrients from captured animals and have specialized adaptations that help it attract, trap, digest and consume prey.
In 1875, naturalist Charles Darwin suggested that two European Saxifraga species might be carnivorous after noticing their sticky hairs and occasional bug victims, but never managed to prove it experimentally.
The newly studied plant is a different species from the pair that Darwin examined, though closely related, but it shares the same insect-trapping structures that inspired his hypothesis.
"We ran multiple tests on this plant and finally confirmed it is a real insect-eating plant. This proves Darwin's guess was correct, and shows how sharp his scientific judgment was," said Hang Sun, a research professor at the Chinese Academy of Sciences' Kunming Institute of Botany and one of the leaders of the study published in the journal Nature Communications.
To determine whether it was actually feeding on insects, researchers used fruit flies raised on food enriched with a stable form of nitrogen.
"Nitrogen is essential for plant growth. Most carnivorous plants live in nitrogen-poor habitats and obtain nitrogen by capturing and digesting insects," Sun said.
After placing the flies onto the sticky hairs, they tracked the movement of the nitrogen through the plant.
The nitrogen they tracked "is ultimately taken into the plant and found throughout the tissues of that plant. That would not happen unless there is uptake or movement into the plant," said botanist and study co-author Douglas Soltis of the University of Florida and the Florida Museum of Natural History.
'KEY TO SURVIVAL'
The captured nutrients did not end up distributed evenly throughout the plant. Instead, the highest levels of prey-derived nitrogen were found in the flowers of Saxifraga candelabrum, a species that reproduces only once during its lifetime.
"Probably needs them for reproductive output. Flowers and seeds. Reproduction is key to survival," Soltis said.
The researchers also found evidence that the plant actively attracts prey. Field experiments suggested that scent plays an important role in drawing insects to its flowers, while tests detected digestive enzyme activity in the glandular hairs, providing further evidence that the plant can break down captured insects.
Catching insects comes with a potential drawback. Many carnivorous plants depend on insects for pollination and risk trapping the very visitors needed for reproduction.
"It is mainly pollinated by relatively large insects like flies. These insects are not held firmly by the sticky glandular hairs and can break away easily. Only much smaller insects get trapped. The plant gains extra nutrients by feeding on these tiny prey while leaving its important pollinators unharmed, allowing successful pollination and reproduction," Sun said.
The plant is the only one from its order known to be carnivorous. But other carnivorous plants may be awaiting discovery. The Qinghai-Tibet Plateau where it resides is home to tens of thousands of flowering plant species.
Sun said some of these may harbor undiscovered insect-trapping abilities.
"Nature finds a way, borrowing a line from 'Jurassic Park.' There are so many innovations in nature — most of which we have not discovered or do not yet understand," Soltis said.
"Many of these innovations are potentially beneficial to human well-being. Exploring that treasure of knowledge can yield enormous benefits."
