Nepenthes: Tropical Pitcher Plants

First, let's get one thing straight: there are no carnivorous plants big enough to eat people, no matter what you've seen on the movie screen. Venus Flytraps top out at about the size of a quarter, and like other carnivorous plants, mainly eat insects. That being said, let's take a look at Nepenthes, the tropical pitcher plants, some of which are large enough to kill small mammals - though that's not what they're really meant to do.

Nepenthes mirabilis, growing in the Savage Garden exhibit at MOSI Outside

Nepenthes (nah-PEN-thees) are found in the Old World tropics, with the highest concentration on Borneo, Sumatra, and the Philippines. Like other carnivorous plants, they have evolved to thrive in areas with poor soils, so their root systems are shallow and some species are even epiphytic (meaning they do not root in soil at all). They are lianas - climbing plants that reach high into the tree canopy to find sunlight. Some nepenthes stems have been known to stretch as long as 50 feet!

Nepenthes Traps and Carnivory

Because the poor soil makes it difficult to get all the nutrition they need, nepenthes have evolved the ability to trap insects and digest them in "pitfall traps". (Learn more about carnivorous plants and their traps here.) At the end of each of the long leaves, a tendril grows, followed by pitcher. Most species have two types of pitchers. Terrestrial pitchers are those at the bottom of the plant, evolved to sit supported by the ground. The aerial pitchers grow higher up the plant, and are generally smaller and often look quite different from the terrestrial pitchers.

The pitchers themselves contain a viscous fluid produced by the plant. The lip of the pitcher, called the peristome, is covered in a slippery waxy substance. Peristomes are often quite colorful, which aids in luring insects in for a closer look. Each pitcher also has a "lid", known as the operculum, which produces nectar to make the plant even more tempting. An insect coming to explore will likely lose its footing on slippery edge and fall into the trap, where the syrupy liquid waits. The insect is unlikely to be able to escape, and the plant's digestive enzymes immediately go to work, breaking down the insect for nutrients.

While insects serve as the main source of prey for tropical pitcher plants, the larger traps sometimes catch bigger victims. Lizards, frogs, and even small mammals like mice or baby birds have been found in nepenthes traps. However, this is not the plant's preferred prey - these organisms are so large that they are likely to rot before they can be broken down, causing damage to the plant.

Unusual Nepenthes Facts

• Nepenthes rajah holds the record for the largest pitcher plant traps. The lower traps of this plant can exceed 41 cm (16 inches) and hold up to 3.5 liters (almost a full gallon) of liquid.

Typical terrestrial pitcher of Nepenthes rajah. Photo by Rbrtjong via Wikipedia.

• In 2009, a new species of tropical pitcher plant was named for famed BBC naturalist David Attenborough. Nepenthes attenboroughii has traps that rival N. rajah in size, and is found in the Phillipines.

• The tendrils of Nepenthes bicalcarata are used by carpenter ants to build their nests. They help the plant by removing larger prey from the pitchers, which may break down too quickly for the plants to absorb the nutrients and instead cause damage to the pitchers.

• Hardewicke's Wooly Bats (Kerivoula hardwickii) roost in the pitchers of Nepenthes hemsleyana. This is a mutualistic relationship, with the bats getting shelter from the plant while the plant receives more than one-third of the nitrogen it needs from the feces of the bats.

• Several nepenthes species have a similar relationship with tree shrews. Nepenthes rajah produces a sweet nectar that lures the tree shrews in. The cups of Nepenthes lowii have evolved to be perfectly sized to allow the shrews to drink the nectar from the lid of the cup while their waste falls into the trap below. Species like these have earned the unflattering but truthful nickname "shrew toilet."

A tree shrew perched on Nepenthes rajah. Photo by Ch'ien Lee via Wikipedia

Growing Nepenthes

Unless you have a greenhouse, growing nepenthes species at home will be very difficult. They require bright light and consistently high humidity (at least 70% and preferably higher), and many cannot tolerate temperatures below 50 degrees F. This is not a plant to be grown on a windowsill or in a sunroom. If you would like more info on growing nepenthes at home, click here.

What's In a Name? 
The genus name Nepenthes is taken from the Greek for "without grief." In Greek mythology, Nepenthe was a drug to cure sorrows, used by Helen in Homer's Odyssey. Edgar Allen Poe later included it in his famous poem The Raven, with his tortured narrator crying out, "Quaff, oh quaff this kind nepenthe and forget this lost Lenore!"

Linneaus chose the name for this genus with this meaning in mind, saying "If this is not Helen's Nepenthes, it certainly will be for all botanists. What botanist would not be filled with admiration if, after a long journey, he should find this wonderful plant. In his astonishment past ills would be forgotten when beholding this admirable work of the Creator!"