Tasha Beenken

Malaysian Plant Life

Nepenthes

Dec. 12th, 2006

 

Nepenthes: Carnivorous Beauties

 

            When traveling to an exotic location such as the rainforests of Borneo it is easy to get lost in the great animal diversity and all of the varying customs of the indigenous people. While it is obvious that the plant diversity is enormous in this region, many may fail to recognize one of the most intriguing groups of plants for which Borneo is known. Nepenthes, otherwise known as pitcher plants, represent a rare and interesting group of carnivorous plants. These plants are known for their odd shaped pitchers and can only be found in a few places in the world. As shown in figure1, Nepenthes are found mostly in Borneo, Malaysia, the Philippines and Sumatra. The greatest diversity is found on the island of Borneo and in Sumatra.

Figure 1. Locations of Nepenthes Growth

Global distribution of Nepenthes.

 

Structure and Digestive Process:

 

            As shown in figure 2, each Nepenthe has a deep fluid-filled cup called the pitcher. The pitcher consists of a digestive zone and a waxy zone. The anatomy of the plant forms a pitfall trap. Insects and other small organisms are attracted to the anthocyanin pigments, usually red, brown, green or yellow, and the promise of nectar (Waltraud). The rim of the cup, called the peristome, has grooves which help to ensure that if insects falls in they cannot climb back out. Many people think that the plant’s digestive enzymes are what kills the insects but in actuality they generally drown in the fluid and are only gradually digested by the fluids after death has occurred. It is not clear what actually causes the digestive action: bacteria washed into pitcher during rainfall or enzymes already in the plant (Waltraud).

            Contrary to popular belief, the lid of the plant does not ever close. It simply acts to stop overflow of the pitcher during heavy rains which occur often in the tropical climates in which pitcher plants are found (Clarke).

Benefits of Carnivorous Activity:

            In the rainforest there are many limitations to growth. There is often a lack of light for plants on the forest floor due to the extensive growth of the tall canopy and its many inhabitants. There is also a lot of competition on the forest floor for the nutrients essential for plant growth (Waltraud). Nepenthes exhibit two forms of growth in order to maximize their growth potential. There are aerial and terrestrial types. The aerial Nepenthes hold considerably smaller amounts of fluid and tend to be much thinner. These modifications allow the plant to more easily climb the trees on which they live. The terrestrial plants tend to be much wider and have much more distinct wings (see figure 2) with pronounced fringe hairs (Clarke).

There are many benefits to which Nepenthes have access to which other plants do not due to the fact that it is carnivorous. Plants need constant access to nitrogen which is a limiting factor in many environments. There are many ways plants have evolved in order to deal with this fact. Some undergo mutually beneficial relationships with nitrogen-fixing bacteria which allow them access to nitrogen from the atmosphere as well as from the soil.  Unfortunately this makes the plant dependent upon another organism its limiting dependencies (Waltraud).

Nepenthes have developed carnivorous feeding habits so that they could independently satisfy their nitrogen needs. By capturing animals, mainly arthropods but occasionally frogs, and lizards, they can increase their nitrogenous stores even during long periods between capturing prey (Waltraud). The captured insects are broken down  into amino acids, peptides, phosphates, ammonium and urea (Orchid Web). This solution is transported throughout the plant in its vascular tissue which is then used for its growth and to produce its secretions (Waltraud). As with most carnivorous plants, these species occur in areas with poor nitrogen supplies in the soil. This gives Nepenthes a distinct growth advantage and a niche which most plants could not occupy without similar mechanisms (Waltraud).

Characterization of Nepenthes found on the Island of Borneo:

 

            Currently there are over 80 species of Nepenthes with one or two characterized each year. Of these, thirty-six species can be found on the island of Borneo. Seven of those species are found only on the island. Many of these plants occur solely on Mount Kinabalu which is the highest mountain in Southeast Asia, 4095 meters above sea level (Whitmore). These carnivorous plants are generally found on mountains exceeding 1000 meters of height; mainly because the energy it takes to form the pitcher is so great it can only compete with other plants if it is in soil with low nitrogen content (Clarke).

    

Nepenthes reinwardtiana                Nepenthes ampullaria

Included are pictures of the seven species of Nepenthes we found while in Sabah and Sarawak, two states in Borneo. We identified them with help from our guides and characterized them using visual inspection. 

Nepenthes reinwardtiana is known for producing aerial and terrestrial pitchers which both lack the wings common to most species of pitcher plants. The pitchers produced by this species are very simple and can reach heights of up to 20 centimeters. On the inner back side of the pitcher, there are two “eye spots” which are common in Borneo species. Scientists still do not know what, if any, function these spots serve but they are clear landmarks when distinguishing between species (Clarke).

Nepenthes ampullaria is identified by its unique growth formations and its peculiar pitcher. This species grows in clusters around the base of plants, as seen in the photo, instead of on climbing stems. The pitchers have been known to grow up to 10 centimeters in height and have very wide bases. The lid tends to be very long and skinny. Unlike most other species, Nepenthes ampullaria’s lid does not cover its pitcher. It tends to feed more on vegetation it degrades which fall into the open pitcher then insects. This may show a step in the evolution of pitcher plants away from their carnivorous origins (Clarke).

Nepenthes xhookereriana                 Nepenthes gracilis

Nepenthes xhookereriana developed naturally as a hybrid of Nepenthes ampullaria and Nepenthes rafflesiana. The terrestrial pitchers tend to mimic the appearance of N. ampullaria with their broad bases and lids. As is noticeable in the photo, the wings of the pitcher are well developed and include pronounced hair-like fringes. Aerial pitchers (not shown) generally lack wings and resemble its more narrow parent species of pitcher plant (Clarke).

The small and graceful Nepenthes gracilis is known for being the most common species of pitcher plant in Borneo. It is generally found in any heath forest or swamp around Kota Kinabalu. One of the reasons for its success is the fact that it can live in many diverse habitats which makes allows it to thrive in many niches found in the tropics of Borneo. The pitchers of this plant tend to be much smaller than the others and are very narrow. They can be green, red, or black. Most of the plants of this species that we photographed were light red in color (Clarke).

            Nepenthes fusca (shown to the left) is found in roadsides leading to and from Kinabalu Park. The tall and narrow pitchers grow up to 20 centimeters in height. The peristome tends to be very dark colored and the body of the pitcher is generally green with large purple and/or black streaks and dots. This is one of the most easily characterized species of pitcher plant because of its unique pitcher pattern (Clarke).

             

 

    

 

 

 

 

 

Nepenthes rajah                               Nepenthes mirabilis        

            The movie star of the Nepenthes family is N. rajah. This species is the most famous of all pitcher plants and is known for its giant pitchers, which can grown up to 35 centimeters in height. Because of its size, these plants are often found on the ground, resting against other objects for support. Its peristome is very pronounced and is scalloped along its edge. Inside there are rows of sharp teeth which make it an especially effective insect trap (Clarke).

Nepenthes mirabilis is known for being unspectacular. This seems unfair to me since its red speckled pitcher is one of my favorite species we saw while in Borneo. The pitchers lack unusual landmarks and are typically found in the lowlands. One distinct characteristic of this species is its thin papery pitcher. While most species feel leathery to the touch this delicate pitcher does not. It can be found in many places from north of the South China Sea all the way to Australia (Clarke).

            The pitcher plants of Sabah and Sarawak are just one of the simple pleasures one can enjoy while discovering the world’s third largest island, Borneo. Terima Kasih!

 

REFERENCES:

 

Clarke, Charles. A Guide to the Pitcher Plants of Sabah. Kota Kinabalu: Natural History

Publications (Borneo), 2001.

 

[Online] Orchid Web. “Nepenthes Culture and Offerings of Pitcher Plants and

Carnivorous Plants.” www.nepenthes.com/nepenthe.htm. Accessed 12-1-06

.

 

Waltraud, Schulze, et al. “Transporters for ammonium, amino acids and peptides are

expressed in pitchers of the carnivorous plant Nepenthes.” The Plant Journal.

1999.

 

Whitmore, T.C. An Introduction to Tropical Rain Forests: 2nd Edition. New York:

Oxford University Press, 1999.