Underground carnivore: the first species of pitcher plant to dine on subterranean prey

"We found a pitcher plant which differs markedly from all the other known species," says Martin Dančák of Palacký University in Olomouc, Czech Republic, lead author of the study, published in the journal PhytoKeys, where his team described the new species.

"In fact, this species places its up-to-11-cm-long pitchers underground, where they are formed in cavities or directly in the soil and trap animals living underground, usually ants, mites and beetles," he adds.

Only three other groups of carnivorous plants are known to trap underground prey, but they all use very different trapping mechanisms and, unlike Nepenthes pudica, can catch only minuscule organisms.

The plant forms specialised underground shoots with entirely white, chlorophyll-free leaves. In addition to lacking their normal green pigmentation, the leaves supporting the pitchers are reduced to a fraction of their normal size. The pitchers, however, retain their size and often also their reddish colour.

"Interestingly, we found numerous organisms living inside the pitchers, including mosquito larvae, nematodes and a species of worm which was also described as a new species," explains Václav Čermák of the Mendel University in Brno, Czech Republic, who was also part of the research team.

The newly discovered species grows on relatively dry ridge tops at an elevation of 1100-1300 m. According to its discoverers, this might be why it evolved to move its traps underground. "We hypothesise that underground cavities have more stable environmental conditions, including humidity, and there is presumably also more potential prey during dry periods," adds Michal Golos of the University of Bristol, United Kingdom, who also worked on this curious plant.

A series of lucky events back in 2012 led to the discovery of the species. Ľuboš Majeský of Palacký University Olomouc, part of the research team, recounts the key moment: "During a several-day trip with our Indonesian colleagues to a previously unexplored mountain, randomly chosen from a number of candidates, we noted plants which were undoubtedly Nepenthes but produced no pitchers. After a careful search, we found a couple of aerial pitchers, a few juvenile terrestrial ones, and one deformed pitcher protruding from the soil."

"At first, we thought it was an accidentally buried pitcher and that local environmental conditions had caused the lack of other pitchers. Still, as we continued to find other pitcherless plants along the ascent to the summit, we wondered if a species of pitcher plant might have evolved towards loss of carnivory, as seen in some other carnivorous plants. But then, when taking photos, I tore a moss cushion from a tree base revealing a bunch of richly maroon-coloured pitchers growing from a short shoot with reduced leaves entirely lacking chlorophyll."

The group then checked the other encountered plants and found that all of them had underground shoots with pitchers, confirming that this species specifically targets the underground environment.

The scientific name Nepenthes pudica points to the plant's curious behaviour: it is derived from the Latin adjective pudicus, which means bashful and reflects the fact that its lower pitchers remain hidden from sight.

Nepenthes pudica is endemic to Borneo. "This discovery is important for nature conservation in Indonesian Borneo, as it emphasises its significance as a world biodiversity hotspot. We hope that the discovery of this unique carnivorous plant might help protect Bornean rainforests, especially prevent or at least slow the conversion of pristine forests into oil palm plantations," concludes Wewin Tjiasmanto of Yayasan Konservasi Biota Lahan Basah, who helped discover the new species.