Ever since Darwin first wrote on carnivorous plants, in his still-fun-to-read 1875 book Insectivorous Plants, there have only been 11 independent origins for plants that eat animals.
Now scientists have discovered a new one, the "North American flowering plant Triantha occidentalis", also known as the "western false asphodel."
The plant has been known for over 100 years — but nobody realized it ate insects. It thrives in damp areas where other carnivorous plants like sundews and butterworts flourish, though, which was one clue.
So recently a group of scientists began examining some T. occidentalis that grow in a provincial park just south of Vancouver. They discovered that the plant is missing some genes for photosynthesis, which was another clue; you normally only see that in plants that are "heterotrophic" and get their energy from sources other than the sun. Also, the stem of T. occidentalis is covered with tiny hairs that are sticky as heck — which could be used to trap insects.
Except … the location of the hairs violated theory. Normally, insect-eating plants put their sticky-trap parts far away from their flowers, because they need some flies to safely reach those flowers, to pollinate them. The fact that T. occidentalis had sticky-trap hairs up the stalk, right up to the flower, didn't add up. That made it seem not carnivorous.
Anyway, there was only one way to figure out if the plants were eating insects: Feed them some!
So they scientist went out into the field, manually put fruit flies on the stems of T. occidentalis — and when they came back a week later, found the flies had been devoured.
Before presenting the flies to the plants, scientists gave each insect a tracking tag. Researchers mixed an amino acid with nitrogen-15, a stable isotope, into the flies' food. If researchers subsequently find the same isotope in plant tissue, it's an indication that they've been transferred from the animals. Using tweezers, Lin affixed the flies, one by one, to the plants' leggy stems, which are dotted with stubby glandular hairs, reddish and sticky as rubber cement.
Lin's team returned to the park after a week, then two, and found stems speckled with exoskeletons. The researchers harvested plants to haul back to the lab. They found that T. occidentalis was indeed siphoning that nitrogen and accumulating it in its stem and fruits. It was clear that the plant was getting energy from consuming the insects, but the researchers aren't sure exactly how they pulled it off. "We didn't examine how they absorbed the nutrients," Lin says. "I suspect they use the glandular hair … but it's just a guess." However the plant managed it, the exoskeletons remained: The plants "can only digest the inner part of the insects," Lin says.
The scientists' paper, paywalled, is here.
As they note, this discovery is really provocative, because it suggests that there may be far more insect-eating plants that we have yet to identify — but which could also be living right under our noses!
Given the existence of Triantha in close proximity to major urban centers on the Pacific coast, our study serves as a vivid reminder that other cryptic carnivores may yet remain to be discovered.
BTW, this is what the plant looks like …
(Photo of T. occidentalis courtesy Wikipedia)