The Carnivorous Plant FAQ v. 12

Q: Nepenthes: the tropical pitcher plants

A: This is arguably the most glorious and spectacular genus of carnivorous plants. These are the plants that fit so many of our stereotypical visions of what a carnivorous plant should be. Many come from steamy jungles in Southeast Asia, they form enormous vines that clamber up to the trees, and their carnivorous traps are great hungry looking maws that, dammit, look carnivorous. You don't need to understand the technical details of this plant to know that it is dangerous to animals!

Furthermore, as if laboring to fit the image, most Nepenthes plants have requirements that make them suitable only for the horticulturist with a lot of greenhouse space. (We will talk more about cultivation in a bit, and I will highlight some species that are relatively easily grown even without a greenhouse. Relatively...)

The first recorded observations on Nepenthes by a westerner are those by Etienne de Flacourt, Governor of a French colony in Madagascar in 1658. The name "Nepenthes" was coined in 1737 by Linnaeus to recall a narcotic (nepenthe) with which Helen of Troy snockered her guests. Most people use the Latin name as a common name, although folks who avoid using Latin verbatim coin ad hoc names such as "tropical pitcher plants" or "monkey cups," ad nauseum. I could enter into ad hominem attacks against such folks, except for the quid pro quo battle that would result. QED.

Nepenthes plants are clambering vines with (usually) long and somewhat unremarkable sword-shaped leaves. At the tip of each leaf is a tendril that often has a little looping twist in it. This twist lets the plant hang onto surrounding vegetation for support. The tendril is tipped by a pitcher---the carnivorous pitfall trap.

The details of the Nepenthes pitchers naturally varies with species. But the general plan is a watertight pitcher with slippery walls that are very difficult for prey to scale once they have fallen inside. The mouth of the pitcher is adorned with a ribbed structure called a peristome. This peristome helps retain prey, and also conducts prey into the pitcher. A pitcher lid hangs over the pitcher opening. This may help keep rain out of the pitcher, but I think its primary function is to attract prey by its attractive coloration and nectar glands. Prey hanging onto the underside of the lid are in extreme danger of plummeting into the pitcher!

It is almost certain that Nepenthes plants produce their own digestive enzymes (called nepenthesin), but this has not quite been proven despite a number of attempts to do so. One thing is certain, though. There are more than 150 species of animals that have learned how to survive in the Nepenthes pitchers, call them home, and probably help in the breakdown of prey captured by the pitchers. In fact, many types of animals, including mosquito larvae, diving ants, crab spiders, and even frogs benefit from close relationships with Nepenthes. It is an extremely interesting field of research.

Nepenthes pitchers usually capture small arthropods. Ones near the ground tend to capture crawling creatures while those higher in the air tend to capture more winged insects (although there is plenty of overlap). Sometimes small vertebrate animals are captured, too. Nepenthes rajah is sometimes cited as capturing little frogs. Did you know that the last thing in a frog to be digested is the skin of its hands? Look in a pitcher of Nepenthes rajah and you can learn about how many frogs it has been eating by looking at the little gloves floating in the juices!

Occasionally, yes, very occasionally larger animals such as very small rodents are captured. But this is rare, and does not really reflect upon the normal course of things. You probably eat the occasional cockroach without knowing about it, but I doubt you would consider them part of your regular diet. (Or would you? Eeek!)

Another interesting feature of Nepenthes, unique among all the carnivorous plants except perhaps the bromeliads, is that plants in the genus are dioecious. This means that the plants make either male flowers or female flowers. It seems that most Nepenthes specimens are male, so female plants are sometimes given a little extra value by those who breed Nepenthes.

Most species of Nepenthes have small ranges located in the Sunda region, that is Borneo, Sumatra, Java, and the Malay Peninsula. However there are interesting exceptions and some of the species have surprisingly extended ranges. The FAQ pages that follow are organized geographically, and in these pages I list all the Nepenthes species that occur in each area. Species may be listed on more than one page if they span the ranges use, so I finish my geographic discussion with a single page that simply lists all the species. (I hope that it is useful for you; it is for me!) I also indicate on my species lists the elevation category for each plant. Those plants that occur at elevations of 0-1000m above sea level are called lowland species, those that occur at elevations higher than 1000m are called highland species. Some species span these categories, so I call them lowland-highland species. This classification system is universal among Nepenthes growers, by the way. To stay as consistent as possible, I used the elevation ranges in McPherson (2009b).

Nepenthes species lists are marvelously controversial. There is by no means universal agreement on species lists, so do not be surprised at discrepencies between my lists and the lists of others. There are several reasons for this. First, Nepenthes can be hard to identify in the first place. Many of the species identifications depend upon pitcher characteristics, but these are not always completely reliable. Furthermore, most species produce "lower pitchers" (near the ground) which are morphologically different from "upper pitchers" (higher on the plant, often produced on flowering stems), and this dimorphism confuses identifications. Finally, all Nepenthes species can hybridize. This complicates things even more.

In his monographic treatment, Danser attempted to organize the genus into several sections. This system was difficult, artificial, and ultimately was abandoned by subsequent researchers in the genus.

When new populations of plants with apparently unique characters is discovered, the various Nepenthes experts around the world almost certainly have differing opinions about how to classify the plants. Some may conclude that the plants represent a newly discovered species. Others may believe they are just variants of a previously known species. Still others may conclude the plants are merely members of a hybrid swarm of other previously known species. But even if the latter, when should a hybrid swarm that has perhaps stabilized in characteristics, be considered a new species? All this is fodder for great screeching matches between ego-bruised scientists, and is enormously fun to watch.

In truth, I am only a spectator of Nepenthes research. I am perfectly happy to acknowledge that I really do not know the answers to many of the complicated questions in Nepenthes taxonomy, nor have I even thought enough about many of the issues long enough to have an authoritative opinion. My ideas are mostly based upon regurgitation of concepts put forth by researchers that I cite.

Page citations: Clarke, C. 1997, 2001; D'Amato, P. 1998a; Danser, B.H. 1928; Frazier, C. 2000; McPherson, S. 2009b; Phillipps, A. and Lamb, A. 1996; Rice, B. 2006a; Schlauer, J. 2002; personal observations.

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Revised: 2018
©Barry Rice, 2018