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Newly discovered carnivorous plant devours underground worms

Found in the tropical savannas of Brazil, Philcoxia minensis uses its sticky underground leaves to trap tiny roundworms.

The carnivorous plant Philcoxia minensis resides in Serra do Cabral, Minas Gerais, Brazil (A), has some of its tiny leaves above ground (B), though most reside below ground (C & D) where they snag wormy snacks for the plant, helping the plant digest its meals.

Rafael Silva Oliveira, PNAS

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Sticky underground leaves help a Brazilian plant to capture and digest worms, a hitherto unknown way for carnivorous plants to catch victims, scientists find.

The rare plant Philcoxia minensis is found in the tropical savannas of Brazil, areas rich in biodiversity and highly in need of conservation. Although some of the plant's millimeter-wide leaves grow above ground as expected, strangely, most of its tiny, sticky leaves lie beneath the surface of the shallow white sands on which it grows.

"We usually think about leaves only as photosynthetic organs, so at first sight, it looks awkward that a plant would place its leaves underground where there is less sunlight," said researcher Rafael Silva Oliveira, a plant ecologist at the State University of Campinas in Brazil. "Why would evolution favor the persistence of this apparently unfavorable trait?"

Researchers suspected the mysterious subterranean leaves of Philcoxia minensis and its relatives were used to capture animals. They share a number of traits with known carnivorous plants — for instance, Venus flytraps possess leaves covered in glands with protruding stalks that help the plant detect prey. Like P. minensis, Venus flytraps also live in nutrient-poor soils, which is apparently why they seek out prey in the first place.

To see if Philcoxia minensis is carnivorous, the scientists tested whether it could digest and absorb nutrients from the many nematodes, also called roundworms, which end up trapped on its sticky underground leaves. They fed the plant nematodes loaded with the isotope nitrogen-15, atoms of which have one more neutron than regular nitrogen-14. Essentially, the scientists placed these Caenorhabditis elegans worms on top of underground leaves of plants kept in a lab setting.


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