When we think of carnivorous plants, we usually think of the clamping maw of the Venus Fly trap, or the rodent-luring pitcher plants — plants that keep their traps safely above ground where we can see them. But the seemingly innocent flowering plants of genus Philcoxia keep their weapons lurking underground, sticky leaves they use to trap and digest nematodes.
Philcoxia, which exists as three species in the Brazilian Cerrado: P. bahiensis, P. goiasensis, and P. minensis, has been a bit of a botanical enigma. In 2000, British botanist Peter Taylor noted that the genus shared certain characteristics with nearby carnivorous plants, such as the stalked capitate glands in the upper leaves. But seeing no evidence of prey, Taylor believed that the leaves had no carnivorous function. Earlier this year, however, in a paper published by the Proceedings of the National Academy of Sciences, a team of researchers from São Paulo's University of Campinas revealed that Philcoxia are indeed carnivorous plants; they simply trap their prey underground.
The team, led by Peter Fritsch of the California Academy of Sciences, placed nematodes labeled with a nitrogen isotope in the plants' soil, and found that, within 24 hours, the plants contained the nitrogen isotope. Philcoxia, as it turns out, has adhesive subterranean leaves that capture passing roundworms. The plants then break down and consume the usable nutrients in the roundworms, leaving behind tiny nematode corpses. This goes a long way toward explaining how the plants are able to survive in the low-nutrient soil of their native region. It's also a reminder that just because you can't see where something keeps its mouth, that doesn't mean it won't try to eat you.
Top image from paper by Pereira et al.