Famous as the rat-trapping pitcher plant, Nepenthes rajah has some of the largest pitchers in the genus Nepenthes.
Nepenthes rajah at Kew Gardens
Nepenthes rajah Hook.f.
Endangered according to IUCN Red List criteria; listed on CITES Appendix I.
Open sites in mossy forests, on ridges or landslips.
Small mammals may drown, and then be digested, if they fall into the large pitchers of this species.
About this species
Nepenthes rajah was named by Joseph Hooker, the second Director of Kew. Perhaps best known for his friendship with Charles Darwin and his writing of the Flora of British India and Genera Plantarum (with George Bentham), Hooker also had a passion for Nepenthes and wrote the first monograph of the genus. 12 species of Nepenthes which were described by him are still recognised today.
Monkeys have occasionally been seen drinking rainwater from Nepenthes species, leading to the use of the common name 'monkey cups' for the genus.
Nepenthes rajah is famous for its large pitchers (urn-like modified leaves), which allow the plants to catch and digest animals. Insects, and in particular ants, make up the majority of prey. However there are reliable observations that, on occasion in the wild, rats have been trapped by this species.
Until recently Nepenthes rajah was a hot contender for the title of 'largest pitchers' in the genus. It is now thought that Nepenthes attenboroughii, discovered in 2007 and named in honour of Sir David Attenborough, may have larger pitchers.
Geography and distribution
This species is native to Sabah (Mount Kinabalu and Mount Tamboyukon), in Malaysian Borneo. It occurs on moist, loose soils between 1,500 and 2,650 m above sea level.
Overview: A shrub, sometimes scrambling. The stem grows up to 3 cm in diameter and normally to 300 cm long (although with support and shady conditions it has been known to grow to 600 cm long).
Leaves: The leaves comprise a sheathed petiole (leaf stalk) 3.5 to 14.0 cm long, a large leathery oblong blade (20 to 50 x 9 to 13 cm) and a long tendril at the end of which is a pitcher (which acts as a pitfall trap).
Pitchers: The leathery pitchers consist of a rugby ball-like cup with a ridged edge and a lid held above. Pitchers are red-purple on the outside and lime green to purple on the inside, ellipsoid in shape, 20-35 x 11-18 cm, but can be up to 40 cm tall. Smaller, funnel-shaped, aerial pitchers may also be produced, but are rare.
Flowers: Produced in large numbers on inflorescences that are usually 60 to 85 cm tall. The brownish-yellow flowers give off a strong, sugary smell. Male and female flowers are borne on separate plants.
Fruits: The orange-brown fruits are 10 to 20 mm long, and produced in large numbers, each with numerous winged seeds.
Only a few hybrids have been artificially produced from Nepenthes rajah, but a number of natural hybrids occur in the wild. One of these is Nepenthes × alisaputrana (N. burbidgeae × N. rajah), which is listed on CITES Appendix II. The natural hybrid N. × kinabaluensis with N. villosa is particularly interesting, since it occurs in large numbers independent of its parents and appears to be self-sustaining and true-breeding, developing into a species in its own right.
Insects are believed to be attracted to nectar produced by large glands covering the pitchers, especially on the lower surface of the pitcher lid. The ridged and toothed edge (peristome) of the pitcher makes it difficult for any animals that fall in to climb back out. They usually die inside the pitcher, drowning in the liquid secreted in its lower half, where they are then broken down by digestives enzymes into nutrients that become available for use by the plant.
Threats and conservation
Nepenthes rajah is considered to be an endangered species, due to its localised distribution. It is thought that most (or perhaps all) of the population occurs within a protected area. The species is currently listed on CITES Appendix I, meaning that trade in wild collected plants is effectively prohibited.
In the early 1980s, plants of Nepenthes rajah were first micropropagated at the Royal Botanic Gardens, Kew, where several novel techniques were devised to facilitate this. Most plants of N. rajah that are in trade today derive from micropropagated material from commercial nurseries, and the illegal trade in plants dug from the Kinabalu National Park, once the only source of supply, is thought to have ceased as a consequence.
This species was introduced into cultivation in 1881, though was then lost for several decades before it was reintroduced. It has been in demand ever since this revival. Advances in tissue culture technology have helped make this species more widely available.
Images of Nepenthes rajah are also used in promotional material to support tourism in Sabah, and in particular in Kinabalu National Park in Borneo.
Nepenthes rajah is cultivated in the Tropical Nursery (one of the behind-the-scenes areas) at Kew, where propagules from the Micropropagation Unit are taken from glass jars and weaned into small rubberised pots. A peat/perlite mix is used as the species requires an acid soil.
Plants are kept warm during the day and cool at night (14 to 16 °C), and misted daily, or twice daily during the summer. Plants benefit from strong lighting, a south facing position and small weekly feeds. The large pitchers that occur in the wild do not currently develop on Kew-cultivated specimens. It is thought this may be the result of the process by which propagules have, over the past 30 years, been selected for suitability for micropropagation, and that the procurement of fresh material may remedy the situation.
This species at Kew
The original specimens collected by Hugh Low on Mount Kinabalu in the 19th century, from which Joseph Hooker named the species, are preserved in the Kew Herbarium. The Herbarium is one of the behind-the-scenes areas of Kew, where preserved specimens are made available to researchers by appointment.
Kew has a large collection (about 200 accessions) of living Nepenthes, maintained for research and conservation purposes. Public access is available mainly through annual visits from the Carnivorous Plant Society. Nepenthes rajah is grown in the Tropical Nursery, one of the behind-the-scenes areas of Kew. It has proved difficult to cultivate plants with the giant pitchers that are seen in the wild, and further research is needed to find out why this is the case.
Kew staff (mainly with Matthew Jebb of Glasnevin Botanic Garden, Dublin) have described 12 new species of Nepenthes and co-authored accounts for identifying the Nepenthes of several areas in the last ten years: European Garden Flora, Flora of China, Flora Malesiana (covering SE Asia), Flora of Peninsular Malaysia (in press) and Flora of Thailand (in prep). A world monograph of the genus is in progress.
Cheek, M. & Jebb, M. (2001). Nepenthaceae. Flora Malesiana 15: 1 - 157. Nat. Herb. Nederland.
Clarke, C., Cantley, R., Nerz, J., Rischer, H. & Witsuba, A. (2000). Nepenthes rajah. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org> (downloaded 15 January 2010).
Hooker, J. (1859). Transactions of the Linnaean Society. 22: 421.
Kew science editor: Martin Cheek
Kew contributors: Sustainable Uses Group; Nick Johnson (HPE)
Copyediting: Emma Tredwell
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