This Flower Hides a Secret: It’s Actually a Carnivore
This wild flower looks innocent. Found in wetlands not far from major cities in the Pacific Northwest, it attracts pollinators with white flowers atop a long sticky stalk. You can even buy seeds of the False Western Asphodel at garden stores.
But according to a new study published Monday in the Proceedings of the National Academy of Sciences, botanists have overlooked a distinguishing feature of the perennial: It is the newest and most unexpected carnivorous plant in the world.
There are 13 known families of carnivorous plants, from insectivorous sundews and Venus fly traps to pitcher plants large enough to drown and devour a mouse. Most live in sunny, humid habitats where essential nutrients are scarce – bogs, acid swamps, jungle canopies – and must feed on live prey.
“Carnivorous plants generally have a strong signal that they are carnivorous,” said Qianshi Lin, a botanist at the University of British Columbia and author of the study. “They usually grow with other carnivorous plants in nutrient-poor environments. And they usually have a structure that can capture insects.
While the Western False Asphodel is found in the types of environments where other carnivorous plants are found, Dr. Lin said, no one suspected that it could be carnivorous as well. “This plant has long been ignored because it has no use and people just don’t know much about it.”
During the summer flowering season, Western False Asphodels produce leafless flowering stems up to 31 inches tall, which are covered in sticky hairs. While herbarium specimens often have small flies or beetles stuck to these hairs, it was generally believed that the hairs were part of the plant’s defense strategy, killing insects that could attack leaves and flowers, a said Dr Lin.
The first clue the plant had an appetite for insects came when T. Gregory Ross, also at the University of British Columbia, noticed markers in the plant’s genetics sometimes associated with carnivorous plants. It was enough for Dr. Lin and his colleagues to take another look.
To prove that a plant is carnivorous, it must be shown that the nutrients travel from the animals to the plant. To test this, Dr. Lin and his colleagues mixed the fruit flies with nitrogen-15 isotopes and placed them on the stems of the false asphodel, as well as the carnivorous sundew and the more harmless wandering fleabane.
When they checked the nitrogen levels of the three plants, Dr Lin said, they found that sundew and false asphodel had taken up roughly the same amount of nitrogen isotopes. And to unhook it, the hairs on the stem of the false asphodel secreted phosphatase, a digestive enzyme that many species of carnivorous plants use to extract phosphorus from insects. The false western asphodel was indeed digesting a prey.
“We found that the nutrients entered the flowers and fruits early on,” said Dr Lin, suggesting that the extra nutrition from the insects helped the plant to reproduce. And while more studies are needed, it’s possible the plant is storing excess insect nutrients in its roots to help with the flowering season the following year.
So far, the Western False Asphodel is unique among predatory plants: no other species uses only flower stems to capture its prey. “Most will avoid having their traps around their reproductive organs, as this will capture or kill their pollinators, which is obviously bad for them,” Dr Lin said. “What this one does is quite unusual.”
To get around this problem, Dr Lin said, the plant’s hairs and secretions appear to be adapted to target only very small prey – mosquitoes and tiny flies – and are likely too weak to accidentally catch a butterfly or bee. .
Western false asphodels may be a further example of how some plants adapt existing structures to carnivory. Plants like sticky purple geranium and tomato also have sticky hairs on their surface, which are generally considered a defense mechanism. But once you’ve trapped insects already, Dr Lin said, it could be a relatively short evolutionary step for plants growing in poor environments to start digesting them.
Does this count as a full-fledged carnivore? Andreas Fleischmann, curator of vascular plants at the Bavarian Natural History Collections, said that in his opinion the main criterion for carnivorous plants is not whether the plant digests insects, but whether it attracts them.
The false asphodel has not yet been shown to actively attract the insects it eats, he said. A large majority of carnivorous plants intentionally attract their prey to specialized leaf traps with a tantalizing scent and striking colors. The false asphodel may represent a different evolutionary strategy: don’t waste the bugs you kill defensively, said Dr Fleischmann.
Either way, the study raises the intriguing possibility that there are other plant species – perhaps even familiar ones – whose ways of digesting insects have yet to be noticed. The Western False Asphodel has three sister species that have not yet been tested and may also be carnivorous.
“It’s a good reminder that we still don’t know much about the ecology of a large number of individual plant species, even in well-known environments,” Dr Lin said.
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