Nepenthes is a genus of carnivorous plants that are also known as tropical pitcher plants. The genus comprises about 170 different species and numerous natural and cultivated hybrids. They have unusual looking pitchers in a variety of colors ranging from black through to red, green and purple. They are sometimes referred to as ‘Monkey Cups’ because monkeys have occasionally been observed drinking the fluid in their pitchers.
Nepenthes usually consist of a shallow root system and a climbing stem. They are rooted in the soil at ground level and use trees and other means of vertical support to climb up to the canopy to get access to well-lit areas of the forest. They can grow up to 15 meters or more and the stem is usually a centimeter or less in diameter. Alternate sword-shaped leaves arise from the stems and a tendril protrudes from the tip of each leaf. In some species this tendril aids in climbing. At the end of each tendril a pitcher forms. The pitcher starts as a small bud and gradually expands to form a globe or tube-shaped trap. The trap produces its own fluid which may be either watery or syrupy and is used to drown the prey. The lower part of the trap contains glands which absorb nutrients from the captured prey. Plants can be propagated by seed, cuttings and tissue culture. When grown from seeds they can begin to root in one to two months and start to form pitchers in about six months. They can live for more than twenty years with the correct care.
Nepenthes are native to parts of South East Asia, India, Madagascar and Australia. The greatest diversity occurs in Borneo, Sumatra and the Philippines with many endemic species. They grow in a range of conditions including humid lowland swamps, steamy jungles and on mountainsides. These environments typically experience high levels of humidity and precipitation and moderate to high levels of light.
Many Nepenthes grow in tropical mountainous regions where they experience warm days but cool to cold humid nights all year round. There are however many exceptions to this such as species that thrive in soils with a high heavy metal content (e.g. N. Rajah) or species that grow on sandy beaches in the sea spray zone (e.g. N. Albomarginata). A few are considered tropical alpine experiencing cool days and nights near freezing.
The leaves of Nepenthes have evolved into ‘fall’ traps that attract prey using a combination of attractive colours, sugary nectar and sweet scents. Surrounding the entrance to the trap is a structure called the peristome (lip) which is slippery especially when wet and this causes the insects to slip and fall into the pitcher. Along the upper inner wall of the trap is a slick, waxy coating which makes it nearly impossible for the prey to escape. Sharp downward pointing hairs force the insect into a pool of fluid at the bottom of the trap.
This fluid contains powerful digestive enzymes that absorb nutrients from the prey. The prey serves primarily as a source of nitrogen and phosphorus for the plant as these are lacking in the nutrient deficient soil in which it grows. The most frequently captured prey of Nepenthes is an abundant and diverse group of arthropods with ants and other insects topping the menu.
Other arthropods frequently eaten include spiders, scorpions and centipedes while snails and frogs are more unusual but not unheard of. The largest species of Nepenthes (e.g. N. Rajah and N. Rafflesiana) may occasionally catch small vertebrates such as rats and lizards. There are even records of cultivated plants trapping small birds.