In the kind of discovery seldom seen in modern biology, scientists say they have discovered a carnivorous Brazilian plant that uses sticky, subterranean leaves to catch and digest worms–an evolutionary strategy for acquiring nutrients that has never before been observed in the plant kingdom.
Researchers say that the rare plant, known to scientists as Philcoxia minensis, has only been found in a handful of increasingly rare savannah regions in inland Brazil.
In a report of their findings published in the online version of the journal the Proceedings of the National Academy of Sciences (PNAS), researchers described the plant, noting that in addition to the thin, millimeter-wide leaves that grow above the earth´s surface, the majority of the plant´s curious leaves grow below the sandy surface, where the its sticky, finger-like projections are used to capture small passing worms.
“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,” explained Brazilian plant ecologist Rafael Silva Oliveira from the State University of Campinas in Brazil to Charles Choi of LiveScience.
The mystery for the researchers, said Oliveira, was “why would evolution favor the persistence of this apparently unfavorable trait?”
Upon closer examination, scientists began to suspect that P. minensis´ bizarre underground leaves might be used for hunting when they noticed that the tiny structures bore a number of similar characteristics in common with other known meat-eating plants. For instance, the Venus flytrap (Dionaea muscipula)–the most well-known of all predatory plants–also has gland-covered leaves which rest upon long stalks and help the animal detect its prey. And like its Brazilian counterpart, Venus flytraps are also found in areas with poor soil, which explains the evolutionary adaptations for obtaining nutrients from an external source.
In order to test their suspicions regarding Philcoxia minensis´ predatory predilections, researchers examined whether it could digest and absorb nutrients from the numerous tiny roundworms known as C. elegans that are often found stuck in its subterranean protrusions. The plant was provided with worms that the scientists had laced with a cocktail containing the isotope nitrogen-15 which can be traced in a laboratory setting.
A subsequent chemical analysis of the plant´s leaves confirmed their suspicions: Significant quantities of nitrogen-15 were discovered inside the sticky leaves of the plant, indicating that the plant absorbed the valuable nutrient from its miniscule nematode prey.
Moreover, the scientists also found chemical traces of enzymatic digestion similar to that known to take place in other carnivorous plants. This makes it highly probably that the nutrients were absorbed directly from the worms rather than from the soil surrounding their decomposing corpses. The researchers believe that the leaves may also release digestive enzymes into the worms after they are captured, making for quick and easy absorption of their nutrients.
What makes these findings particularly exciting for evolutionary biologists is that they seem indicate multiple, independent evolutionary pathways by which predatory plants came into existence.
“I personally think these findings also broaden up our perception about plants,” added Oliveira.
“They might look boring for some people because they don´t move or actively hunt for their food, but instead, they have evolved a number of fascinating solutions to solve common problems, such as the lack of readily available nutrients or water. Most of the time, these fascinating processes of nutrient acquisition are cryptic and operate hidden from our view.”
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