Nepenthes rajah Hook.f. (Nepenthaceae)


Giant Bornean pitcher plant

Lithograph of Nepenthes rajah from 'Curtis's Botanical Magazine' (1905; t. 8017). Nepenthes specimen collected from Sri Lanka in the 1680s by Paul Hermann (Oxford University Herbaria).

Described as 'one of the most striking vegetable productions hither-to discovered' by Joseph Hooker, Nepenthes rajah deserved the appreciation of one of the world's great nineteenth-century botanists. A scrambling, insectivorous plant, the shaded stems of the 'King of the Nepenthes' can be up to six metres long. At the end of their leaves, Nepenthes rajah has long been considered to have the largest of all Nepenthaceae; the scarlet, nectar-secreting vessels act as pit fall traps and nurse a liquid cocktail of enzymes and detritus. Equally dramatic, Nepenthes rajah produces large racemes of male or female flowers that, in some cases, can be more than one metre long. The dull brown-yellow flowers exude enticing, sugary-sweet fragrances that attract insects.

Nepenthes rajah lures more than just insects. Often nicknamed the 'monkey cups' genus, it is believed the pitcher contents of Nepenthes are prized beverages for primates. There have even been reports of small rodents found drowning or decomposing in Nepenthes rajah pitchers. However, contrary to urban legend, Nepenthes rajah enjoys a somewhat less fatal mutualistic relationship with mountain tree shrews and summit rats. These mammals straddle the pitcher mouth to feast on the nectar produced on the underside of the pitcher lid. When they defecate the pitcher acts like a potty, the faeces enriching the pitcher fluid with nitrogen and phosphorus. In the case of the shrew, the distance from the pitcher mouth to the nectar is similar to its average body length.

The combination of collection trends and habitat destruction means natural populations of this majestic beauty are confined to Mount Kinabalu and Mount Tamboyukon, Borneo. Nepenthes rajah is now a CITES Appendix 1 listed species, that is, all wild collection of and trade in Nepenthes rajah is prohibited. However, thanks to advances in micropropagation, it is now possible to produce successfully large numbers of Nepenthes rajah at low cost, meaning pressure from illegal wild collecting has been reduced. Strangely, growing Nepenthes rajah in jars occasionally produces unusual specimens; the pitcher size of micropropagated Nepenthes is considerably more variable than found in the wild.

The scarcity and plight of Nepenthes rajah has been noticed and exploited. Its image is used to encourage tourism, bringing money into areas of Sabah, particularly the Kinabalu National Park. With efforts of conservationists, and the enforcement of conservation legislation, this striking 'vegetable production' is likely to continue to inspire awe and provoke interest across the world.

Further reading

Greenwood M et al 2011. A unique resource mutualism between the giant Bornean pitcher plant, Nepenthes rajah, and members of a small mammal community. PLoS ONE 6 e21114.

Simpson R 1991. Plants in peril. 15. Nepenthes rajah. Curtis's Botanical Magazine 8, 89-94.

Simpson R 1995. Nepenthes and conservation. Curtis's Botanical Magazine 12, 111-118.

Jess Lee