This plant eats meat. Image: Danilo Lima
Scientists have discovered a new lineage of flesh-eating plants that lurks in bogs next to major metropolitan areas of the Pacific Northwest, reports a new study. The herb, Triantha occidentalis, was previously known to science, but its meat-eating proclivities were identified for the first time during field expeditions to Cypress Provincial Park, which is just north of Vancouver, British Columbia.
In addition to being minted as the 12th known example of independent evolution of carnivory in plants, T. occidentalis also proved to be “unique among carnivorous plants and unexpected based on theory,” according to a study published on Monday in the Proceedings of the National Academy of Sciences. “We are all very excited,” said Qianshi Lin, who led the new study while he was a doctoral student at the University of British Columbia (UBC), in an email. “It's very rare to find a new origin of carnivory.” “Before our finding, over the past two decades, only one new example of carnivory has been found,” added Lin, who is now a postdoctoral fellow in biology at the University of Toronto Mississauga.Lin and his advisor Sean Graham, a professor of botany at UBC who co-authored the new research, were motivated to search for carnivory in T. occidentalis due the intriguing results of 2016 study, also co-authored by Graham, which found that Triantha lacks a gene that has been lost in other carnivorous plant species. This genetic similarity to certain botanical meat-eaters was not the only clue that T. occidentalis might be munching on bug flesh. The plant also grows sticky hairs on its stems that trap small insects, and it thrives in the kind of nutrient-poor environments typical of carnivorous plants. All of these factors suggested the herb could be “cryptically carnivorous,” according to the study, inspiring the researchers to seek it out in bogs for closer inspection.
During field experiments conducted in August 2018, Lin attached dead fruit flies to the sticky stems of wild herbs at Cypress Provincial Park. Prior to being fed to T. occidentalis, the flies were metabolically stamped with heavy nitrogen isotopes that allowed the researchers to track how much of this key nutrient the plant might be consuming from its insect prey. The results revealed that T. occidentalis received as much as 64 percent of its nitrogen intake from bug flesh, distinguishing it as a bonafide carnivore, according to models developed by colleagues at the University of Wisconsin–Madison who co-authored the new study. “We did expect Triantha to be carnivorous according to the former genomic study and their sticky hairs,” Lin said. But though “the results were what we expected” they are “still very exciting,” he added.Indeed, T. occidentalis is not only an extremely rare addition to the “small but fascinating ecological guild of carnivorous plants,” in the words of the new study, it is also very different from almost all other known members of this exclusive group. Most carnivorous plants keep their bug traps and flowers at a healthy distance to ensure that they don’t kill the pollinating insects that help them reproduce. The flowers of T. occidentalis, in contrast, grow near the sticky traps on its stems, which runs counter to theories about the anatomy of carnivorous plants.
The team concluded that the plant’s traps may have evolved to ensnare very lightweight insects, such as midges and gnats, while leaving larger and stronger pollinators, like bees and butterflies, free to come and go as they please. The unusual strategy hints at a previously overlooked mode of carnivory in plants that Lin and his colleagues hope to explore further, including in Triantha species that grow in Wisconsin.“We would like to check if other species in this genus are also carnivorous,” Lin said. “We also want to look deep into their genome to see what makes them carnivorous.” T. occidentalis occupies a wide range across the West Coast, so it’s impressive that its taste for insect flesh has flown under the radar for so many years. The new study may be a sign that carnivorous plants are more common than previously assumed—and that they may be chowing down on insects in a habitat near you.“The fact that T. occidentalis was hidden in plain sight as a carnivorous plant, despite its proximity to several major urban centers on the Pacific coast of North America, is remarkable,” concluded the team in the study. “This serves as a reminder that other cryptic carnivores may yet remain to be uncovered and that much is still to be learned about the ecology of individual plant species, even in relatively well-known floras.”