Pitcher plant (Nepenthes argentii)
|Size||Height: c. 30 cm (2)|
Classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (3)
This charming tropical pitcher plant is the smallest species of Nepenthes, a spectacular genus of carnivorous plants. Nepenthes argentii is a vine that creeps along the ground, with a long, vertical, underground rhizome (4). Because of its small size, Nepenthes argentii is usually concealed in shrubbery, and is only usually detected by the inflorescences emerging above the shrub canopy (2). Thimble-sized, deep maroon-pink pitchers, formed from modified leaves, hang from coiled tendrils. Nepenthes species usually have two or three different types of pitcher, generally known as upper and lower pitchers (5). The pitchers contain an acidic fluid, secreted by the many glands which cover the inside surface of the lower half of the pitcher (5). The smooth and waxy upper inner surface of the pitcher makes it impossible for invertebrates that have fallen into the pitchers to gain a foothold (5), and a ridge of hardened tissue lining the mouth of the pitcher, the peristome, bears downward pointing teeth, also preventing insects from escaping. A lid overhanging the mouth of the pitcher prevents rain water from diluting the pitcher fluid (6). The peristome of Nepenthes argentii is dark purple and the lid is spotted red underneath and mostly mottled red on top (2). The lower surface of the leaves and tendrils of this species are covered with red hairs (2).
Endemic to the Philippines where it occurs in the Sibuyan and Romblon Provinces (1).
Nepenthes argentii inhabits sub-alpine shrubbery on igneous rock, at an altitude of around 1,400 metres (1).
Pitcher plants are dioecious, meaning that male and female flowers grow on separate plants and only begin to flower once the upper pitchers are produced (5) (6). 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 the fruits of Nepenthes species usually take about three months to develop and ripen. Nepenthes argentii has been observed fruiting in August (2), producing fruits that each contain between 100 and 500 very light, winged, seeds, which are thought to be dispersed by the wind (5) (6). Despite enormous numbers of seeds being produced, only a few manage to germinate and only a fraction of those survive to maturity (6).
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. 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 (5). Despite the hostile environment of the pitchers, they can be home to number of animals, such as mosquitoes, which emerge from larvae that live in the pitcher fluid (6).
Nepenthes species are threatened by a combination of over-collection and habitat loss (6). The highly restricted range of Nepenthes argentii makes it particularly susceptible to the impacts of habitat disturbance or catastrophic environmental events, such as drought and fire. In addition, highland plants, such as Nepenthes argentii, take longer to recover from any disturbance than lowland plants as growth is slower (7).
Although listed under Appendix II on the Convention on International Trade in Endangered Species (CITES) which limits the international export of this species (3), 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 (6). Nepenthes argentii is becoming more common in cultivation, helping to reduce the impact on wild populations (6).
For more information on Nepenthes species see:
- Clarke, C. (1997) Nepenthes of Borneo. NaturalHistory Publications, Kota Kinabalu, Malaysia.
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- Carnivore: flesh-eating.
- Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
- Enzymes: Proteins that trigger, or accelerate, activity in the cells of the body, for example, breaking down foods during digestion, and building new proteins.
- Fertilisation: in a flowering plant, fertilisation is the process of a pollen grain joining with the ovule (female egg cell). After fertilisation, the female parts of the flower develop into a fruit.
- Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
- Igneous rock: rock formed when volcanic magma cools.
- Inflorescences: the shoots of a plant which bear a group or cluster of flowers.
- Invertebrates: animals with no backbone.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Photosynthesis: metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.
- Pollination: the transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
- Rhizome: thickened, branching, creeping storage stems. Although most rhizomes grow laterally just along or slightly below the soil's surface, some grow several inches deep. Roots grow from the underside of the rhizome, and during the growing season new growth sprouts from buds along the top. A familiar rhizome is the ginger used in cooking.
IUCN Red List (December, 2009)