First carnivorous plant to grow underground pitfall traps discovered

A pioneering pitcher plant is changing what we know about carnivorous species.

With a name meaning 'shy', the pitcher plant Nepenthes pudica hides its traps under moss or soil to capture a range of prey including ants, mites and beetles. While other plants that eat subterranean life have previously been discovered, N. pudica's pitfall traps are currently unique in the botanical world and allow it to catch much larger prey.

This unique plant, however, could already be under threat. Only living in one small area of Indonesia, scientists believe this unique plant should be classed as Critically Endangered. 

Wewin Tjiasmanto, who helped to discover and describe the new species, says, '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.'

The description of N. pudica was published in the journal PhytoKeys. 

What are pitcher plants?

Pitcher plants are a type of carnivorous plant which have modified their leaves to produce large, jug-shaped structures which give the plants their name. 

True pitcher plants come from one of two families, either the Sarraceniaceae found in the Americas, or the Nepenthaceae from across southeast Asia, Australasia and Madagascar. 

Insects and other prey are lured to the plants by nectar and attractive scents, causing the victims to land on the edge of the pitcher. Condensation and nectar make this surface slippery, causing the insect to fall into the fluid filled pitcher.

Once inside, it is almost impossible for prey to escape. The interior of the pitcher can be formed of slippery scales, hairs or folds that make it difficult to climb out, while species such as Sarracenia flava can use compounds such as coniine which paralyse insects.

The prey are then consumed using digestive enzymes, and the plant uses the resulting nutrients to grow. In order to attract prey, these pitchers are normally set above the ground, especially when bright colours are used as part of the lure. 

Some pitcher plants, however, grow closer to the ground. The parrot pitcher plant, Sarracenia psittacina, lures in ground dwelling insects with nectar and then forces them onwards into the digestive tract with hairs that prevent the prey from moving backwards.

N. pudica takes things one step further by burying its pitchers in the soil. 

How was the underground pitcher plant discovered?

The plant was first discovered a decade ago in 2012, when researchers exploring a previously unsurveyed mountain came across pitcher plants that appeared to have lost their pitchers.

Co-author Dr Ľuboš Majeský says, '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. As we continued to find other pitcherless plants, we wondered if a species of pitcher plant might have evolved towards losing its carnivory.'

'But then, when taking photos, I tore a moss cushion from a tree base and revealed a bunch of richly maroon-coloured pitchers with reduced leaves that entirely lacked chlorophyll.'

The underground pitchers are unlike those of other pitcher plants. Generally, pitchers are quite fragile, but N. pudica's have developed thicker walls that allow them to push soil apart as they grow.

Burying these structures underground may protect the plant against the dry conditions that are found in its montane habitat, where it lives between 1100 and 1300 metres above sea level. The researchers also believe that growing them underground also increases the plants access to prey, as burrowing insects dig down to find more stable conditions.

While the pitchers provide the plants with food, they can also act as a home for some species. Mosquito larvae, nematodes and annelid worms have been found living inside N. pudica, including Pristina armata, a worm measuring less than one millimetre that may live its entire lifecycle inside the pitcher.

This unique biodiversity, however, may be under threat. The rainforests of Borneo are threatened by a range of factors, including conversion to palm oil plantation and the construction of the new Indonesian capital, Nusantara.

While N. pudica lives in the mountainous regions of the island, which form part of the Heart of Borneo conservation initiative, it lies just outside the boundaries of the Kayan Mentarang National Park. As the plant is believed to live in an area of less than four square kilometres, any impact on its home could see it quickly wiped out.

The researchers have called for further protections for the area as they continue to investigate Borneo's flora, including what might represent another species of underground pitcher plant located in the island's east.

In time, more specialist carnivores could be described if the rainforests that support them survive long enough for the plants to be discovered.