Pitcher plant  (Nepenthes ovata)

This spectacular carnivorous plant traps and digests invertebrates in large, colourful pitcher-shaped leaves. Nepenthes ovata is a vine with modified pitcher-shaped leaves hanging from coiled tendrils, which either climbs up small trees to a height of about five metres or creeps along the ground depending on the surrounding vegetation (2). Nepenthes species usually have two or three different types of pitcher, generally known as upper and lower pitchers (4). In Nepenthes ovata the lower pitchers are trumpet-shaped and green, occasionally blended with red, with a dark red rim that may be streaked with green. The upper pitchers are broadly cylindrical and are yellow with a red rim and yellow stripes (2). Insects and other invertebrates fall into the pitchers, which contain an acidic fluid secreted by the many glands that 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 captive insects to gain a foothold (4), and a ridge of hardened tissue lining the mouth of the pitcher, the peristome, bears pronounced downward pointing teeth, also preventing insects from escaping. A lid overhanging the mouth of the pitcher prevents rain water from diluting the pitcher fluid (2) (5).

Endemic to Mount Pangulubao and Mount Lubukraya in northern Sumatra, Indonesia (2) (7).

Found in wet, mossy forest at an altitude of 1,800 metres, Nepenthes ovata is often found growing amongst Sphagnum moss with the vines climbing into small trees if they are growing in the area. Nepenthes ovata tends to creep along the ground on Mount Pangulubao and grows primarily as an epiphyte on Mount Lubukraya (2) (7).

Pitcher plants are dioecious meaning that male and female flowers grow on separate plants (6), and only begin to flower once the upper pitchers are produced (7). 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) (5). Despite enormous numbers of seeds being produced, only a few manage to germinate and only a fraction of those survive to maturity (5).

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 (6). 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 (6).

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 (5).

Tropical pitcher plants, such as Nepenthes ovata, are threatened primarily from habitat destruction, but due to their low numbers, collecting has also had serious impacts on the population (2). In Indonesia, habitat destruction is a major problem as a result of illegal and commercial logging and large agricultural projects, such as rubber and oil palm plantations (8). Sumatra has a very high rate of habitat loss, with some areas losing up to 65 percent of their forest cover in the last 25 years (9). Only 33.8 percent of Sumatra remains covered by primary forest, and only 1.3 percent of this is upper montane vegetation, in which Nepenthes ovata is found. The highly localised distribution of this Nepenthes species makes it particularly susceptible to the impacts of habitat disturbance or catastrophic environmental events, such as drought or fire. In addition, highland plants, such as Nepenthes ovata take longer to recover than lowland plants from any disturbance, as growth is slower (2).

All Nepenthes species are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) restricting international trade. However, the incidence of illegal trade in Nepenthes is high, as it is very difficult to regulate and Nepenthes species do not need to be labelled down to species level. Urgent attention is required to remedy this and other trade loopholes (2) (5). Nepenthes species, including Nepenthes ovata, are being increasingly cultivated, which helps 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 establishment of habitat reserves (10).

For more information on Nepenthes species see:

• Clarke, C. (2001) Nepenthes of Sumatra and Peninsular Malaysia. Natural History publications, Kota Kinabalu, Malaysia.

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk