Pitcher Plant

Pitcher plants are dioecious, meaning that male and female flowers grow on separate plants (4), and only begin to flower once the upper pitchers are produced (5). The flowers produce large amounts of nectar during the early evening and night, which evaporates by morning. This nectar attracts flies during the early evening and moths at night to aid pollination. Once fertilised, a fruit usually takes about three months to develop and ripen. The fruits of Nepenthes species produce between 100 and 500 very light, winged seeds, which can measure up to 30 millimetres long, and are thought to be dispersed by the wind (2) (6). Despite enormous numbers of seeds being produced, only a few manage to germinate and only a fraction of those survive to maturity (2). Carnivorous pitcher plants are adapted to grow in soils low in nutrients. Although the plants do gain some nutrition through the soil, and energy through photosynthesis, they supplement this with a diet of invertebrates, usually consisting of ants, cockroaches, centipedes, flies and beetles (4). Insects are attracted to the pitchers by their bright colours and nectar, which is secreted by glands situated on the lid and the peristome of the pitcher. The insects fall into the acidic fluid at the base of the pitcher and, unable to escape, they drown. Digestive enzymes are then released to break down the captured prey (4). Despite the hostile environment of the pitchers, they can be home to number of animals. The red crab spider (Misumenops nepenthicola) inhabits pitcher plants in Malaysia, Indonesia and Singapore. This spider ambushes insects that crawl into the pitcher and preys upon other insects, such as mosquitoes, as they emerge from larvae that live in the pitcher fluid (2).

Nepenthes dubia is listed under Appendix II of the Convention on International Trade in Endangered Species (CITES) limiting the international export of this species (3). However, trade is very difficult to regulate. There is no requirement for internationally traded Nepenthes to be identified down to species level and plants simply labelled as Nepenthes accounted for 94 percent of all exported Nepenthes plants between 1988 and 1993. This needs to be remedied and urgent attention is required to close other trade loopholes (2). Nepenthes species, including Nepenthes dubia, are being increasingly cultivated, helping to reduce the impact on wild populations. Conservation efforts can be made more effective not only by the implementation and enforcement of protective laws, but also by the encouragement of artificial propagation and the establishment of habitat reserves (8).

This beautiful carnivorous plant is a vine which grows to a length of about three metres and has modified pitcher-shaped leaves that hang from coiled tendrils (2). The trumpet-shaped pitchers of Nepenthes dubia are usually light green to yellow, although orange and red forms are also known (2). The pitchers contain an acidic fluid, secreted by the many glands which cover the inside surface of the lower half of the pitcher (4). The smooth and waxy upper inner surface of the pitcher makes it impossible for insects that fall into the pitchers to gain a foothold (4), and a ridge of hardened tissue lining the mouth of the pitcher, the peristome, bears downward pointing teeth, also preventing insects from escaping (2). A lid overhangs the mouth of the pitcher preventing rain water from diluting the pitcher fluid (2). In most plants the stem, inflorescence and tendrils are characteristically purplish-red (2). There is some debate whether Nepenthes dubia is a distinct species or whether is it a hybrid between N. inermis and N. bongso (5).

Nepenthes dubia grows epiphytically in lower montane forest and either epiphytically or terrestrially on clumps of moss in stunted upper montane forest (2).

Endemic to central Sumatra, Indonesia, where it is found only on Mount Talamau between 1,800 and 2,700 metres above sea level (2) (5).

Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1), and listed on Appendix II of CITES (3).

Nepenthes species are threatened by a combination of over-collection and habitat loss (2). The biodiversity of Indonesia is significantly threatened by widespread habitat destruction, caused by illegal and commercial logging and large agricultural projects such as rubber and oil palm plantations (7). The Critically Endangered Nepenthes dubia has a highly localised distribution, growing on only one mountain, making itparticularly susceptible to extinction through habitat destruction or catastrophic environmental events, such as drought or fire. In addition, montane species, such as Nepenthes dubia, take longer to recover than lowland plants after such events, as growth is slower (2).