Pitcher plant: a taste for flesh

Plants, we are told in school, are very different from animals. Plants, they tell us, do not move, do not breathe oxygen and get their nutrients from the soil. Animals on the other hand need to eat plants and other animals to survive. Most of us grow up with the idea that plants are quite stupid, and that animals are the dominant kids on the block.

Pitcher plants on top of Mahe Mountain © James Hardcastle This fly is heading for its end © Gideon Climo Pitcher plant's victim being digested © James Hardcastle

However, high up on the hills of Mahe is a plant that defies many of our prejudices; a rebel of the botanical world which does things its own way. This plant gets its food from animals that it attracts, captures, kills and digests. This voraciour, meat-eating “vegetable” is called a Pitcher plant or “Lyan potao” in kreol. Although this species of pitcher plant, Nepenthes pervelli in Latin is found only in Seychelles, pitcher plants of the genus Nepenthes occur in various parts of the world.

Of the 75 species of Nepenthes in the world, most are found in South East Asia. In our part of the world, one species is found in India, another in Sri Lanka, two in Madagascar and one species in the Seychelles. there are none in Africa. The Seychelles are at the end of the geographical distribution range of Nepenthes pitcher plants. When the super continent known as Gondwanaland shook itself apart hundreds of million years ago, the Seychelles were wrenched away from Madagascar, India and Sri Lanka. Hence the geographical origin of the Seychelles pitcher plant. Here in Seychelles the best stands of pitcher plants are found on some high hills of Mahe and especially in the mist forests of Silhouette.

The peculiar carnivorous habit of the pitcher plant turns it into a genuine botanical curiosity. There are other families of carnivorous plants around the world but they form a small minority of all plant species. Why should a small group of plants have developed a taste for flesh when the majority of plants species have not? The answer is that pitcher plants like other carnivorous plants live in nutrient- poor soils.  Many habitants in Seychelles are poor in nitrogen and phosphorus, two elements that are vital for plants. Pitcher plants extract these goodies from the bodies of animals that are trapped inside their fantastic structures.

The pitchers are modified parts of leaves and arise when the leaves are young. In a juvenile pitcher the lid is firmly closed and the walls of the pitcher plant are soft. As the pitcher matures, the walls get firmer and the inside gets filled with fluid secreted by the plants. When the pitcher is fully  charged, the lid opens, there is a popular belief that the lid closes upon its prey. This is not so. The lid is a multi purpose device although it cannot move. It blocks the opening of the pitcher until it is fully charged with fluid. It also is a seduction device, attracting insects with its bright colours. The lid can also from a canopy over the pitcher preventing rain from filling it up.

A pitcher has various parts. The rim has a collar containing nectar -  secreating glands. The inside of the pitcher has a waxy zone that offers a slippery surface to any unwary animal visitor. The bottom of the pitcher plant is full of acidic, digestive fluid.

An insect is first attracted to the pitcher by the colourful lid. It is then seduced and tricked into climbing inside the pitcher by nectar-producing glands in the collar. The unfortunate victim then finds to its horror that it cannot find a footing on the waxy zone and falls in the acidic fluid. Enzymes similar to those in the human stomach break down the animal tissues and the end products absorbed through the walls. The decomposition of insects in the pitcher is not only a result of enzymes but also due to the action of organisms that live unharmed inside the pitcher. In fact some of these organisms are found nowhere else but inside pitcher plants. A unique Seychelles mosquito breeds inside these structures. Experiments have shown that this species of mosquito will lay its eggs only in the pitchers. Another organism found uniquely in this environment is a microscopic  mite. There may be hundreds of these mites in a single pitcher. Somehow these organisms have coevolved with pitcher plants over millenia and are not affected by the acidic digestive juices. They form an amazing ecological community that exists on the remains of prey in the pitcher.

How did such bizzare plants come about? Scientists believe that millions of years ago the ancestors of pitcher plants resembled primitive ferns and bromeliads that live in nutrient poor environments. These plants such as the common Seychelles fern known as Langdebef, have rosettes of leaves shaped like funnels. They catch debris and detritus including small insects from above. These ferns do not digest animals but their decomposing bodies add to the fern’s meagre store of nutrients. Through the course of evolution, plants became more and more adapted to capturing and utilising the bodies of animals.

So, if insects are attacking and killing your favourite plant out there in your garden, take heart and remember that some plants have  turned the tables on insects and capture and devour the little bugs.

Facts:

Scientific name: Nepenthes pervillei

Creole name: lalyan potao
Localities recorded: Mahe, Silhouette
Description: endemic woody climber with rosettes of leathery ovate leaves to 25 cm long, the midrib extended to form a tendril or a vertically held funnel shaped pitcher to 15 cm tall with a lid. The brownish cream and flowers are in loose clusters on erect separate stalks to 25 cm tall and the fruit are clubshaped capsules to 1.5 cm long.