Nepenthes rajah is a carnivorous pitcher plant species of the family Nepenthaceae. It is endemic to Mount Kinabalu and neighbouring Mount Tambuyukon in Sabah, Malaysian Borneo. Nepenthes rajah grows exclusively on serpentine substrates, particularly in areas of seeping ground water where the soil is loose and permanently moist. The species has an altitudinal range of above sea level and is thus considered a highland or sub-alpine plant. Due to its localised distribution, N. rajah is classified as an endangered species by the IUCN and listed on CITES Appendix I.
The species was collected by Hugh Low on Mount Kinabalu in 1858, and described the next year by Joseph Dalton Hooker, who named it after James Brooke, the first White Rajah of Sarawak. Since being introduced into cultivation in 1881, it has always been a sought-after species, although costly and hard to cultivate. Tissue culture has allowed it to become more widespread in cultivation.
N. rajah is best known for the giant urn-shaped traps it produces, which can grow up to highHamilton, G. 2011. The Sabah Society. and wide.McPherson, S.R. 2009. Pitcher Plants of the Old World. 2 volumes. Redfern Natural History Productions, Poole. These are capable of holding of water and in excess of of digestive fluid, making them probably the largest in the genus.
N. rajah can trap mammals as large as rats.Phillipps 1988, p. 55. N. rajah occasionally traps small vertebrates such as frogs, lizards, and even birds. Insects, and particularly ants, are its staple prey. The pitchers are host to many other organisms, some so specialised that they cannot survive anywhere else, and are called nepenthebionts. N. rajah has two such mosquito taxa named after it: Culex rajah and Toxorhynchites rajah. The species is able to hybridise in the wild with all other locally occurring Nepenthes species.
Etymology
Joseph Dalton Hooker described Nepenthes rajah in 1859, naming it in honour of James Brooke, the first White Rajah of Sarawak.Kurata 1976, p. 61. 'Rajah Brooke's Pitcher Plant'Phillipps & Lamb 1996, p. 129. is an accurate, but seldom-used common name. N. rajah is sometimes called the 'Giant Malaysian Pitcher Plant'Gibson 1983. or simply 'Giant Pitcher Plant', although the binomial name remains by far the most popular way of referring to this species. The specific epithet rajah means "King" in Malay and this, coupled with the impressive size of its pitchers, has meant that N. rajah is often called the "King of Nepenthes".Steiner 2002, p. 94.
Plant characteristics
Nepenthes rajah is a scrambling vine. The stem usually grows along the ground, but climbs whenever it comes into contact with a suitable support. The stem is up to ) thick and may reach up to in length, although it rarely exceeds . The leaves are distinctive and reach a large size. They are leathery in texture with a wavy outer margin. The leaves are characteristically peltate, whereby the tendril joins the lamina on the underside, before the apex. The tendrils are inserted within below the leaf apex and reach a length of approximately .
Pitchers
The pitcher is a trap consisting of the main pitcher cup, covered by an operculum or lid. A reflexed ring of hardened tissue, the peristome, surrounds the entrance. N. rajah produces two distinct types of trap. "Lower" or "terrestrial" pitchers, the most common, are very large, richly coloured, and ovoid in shape. Exceptional specimens may be more than in length and hold of water and over of digestive fluid, although most do not exceed .Clarke 2001b, p. 7. The lower pitchers rest on the ground. They are usually red to purple on the outside, lime green to purple on the inside.Clarke 2001b, p. 26. Mature plants may in addition produce much smaller "upper" or "aerial" pitchers, which are funnel-shaped, and usually more colourful. The tendril attachment is normally at the rear of the pitcher cup. True upper pitchers are rare, as the stems rarely attain lengths greater than a few metres before dying off.Clarke & Kruger 2005.
The peristome has a distinctive scalloped edge and is greatly expanded, forming a red lip around the trap's mouth. A series of raised ribs intersect the peristome, ending in short, sharp teeth that line its inner margin. The inner portion of the peristome accounts for around 80% of its total cross-sectional surface length. The huge, vaulted lid is a distinguishing feature of this species. It is ovate to oblong in shape with a distinct keel down the middle, and two prominent lateral veins. Schmid-Hollinger, R. N.d. Kannendeckel (lid) . bio-schmidhol.ch. The spur at the back of the lid is approximately long and unbranched.
The plant has very large nectar-secreting glands covering its pitchers. The inner surface of the pitcher is wholly glandular, with .Danser 1928, 38.
Flowers
N. rajah seems to flower at any time of the year. Flowers are produced in large numbers on inflorescences that arise from the apex of the main stem. N. rajah produces a very large inflorescence that can be , and sometimes even tall. The individual flowers of N. rajah are produced mainly in pairs on reduced partial peduncles and so the inflorescence appears superficially like a raceme, though it is technically a racemose panicle, that is, a panicle with branching so greatly reduced as to appear raceme-like. The flowers are reported to give off a strong sugary smell and are brownish-yellow in colour. Sepals are elliptic to oblong and up to long. Like all Nepenthes species, N. rajah is dioecious, which means that individual plants produce flowers of a single sex. Fruits are orange-brown and long . A study of 300 pollen samples taken from a herbarium specimen (J.H.Adam 2443, collected at an altitude of ) found the mean pollen diameter to be (SE=0.3; CV=7.0%).Adam, J.H. & C.C. Wilcock 1999. Pertanika Journal of Tropical Agricultural Science 22(1): 1–7.
Carnivory
N. rajah is a carnivorous plant of the pitfall trap variety. It is famous for occasionally trapping vertebrates, even small mammals. There exist at least two records of drowned rats found in N. rajah pitchers. The first observation dates from 1862 and was made by Spenser St. John, who accompanied Hugh Low on two ascents of Mount Kinabalu. In 1988, Anthea Phillipps and Anthony Lamb confirmed the plausibility of this record when they managed to observe drowned rats in a large pitcher of N. rajah. In 2011, a drowned mountain treeshrew (Tupaia montana) in a N. rajah pitcher was reported. N. rajah occasionally traps other small vertebrates, including frogs, lizards and even birds, although these cases probably involve sick animals, or those seeking shelter or water in the pitcher, and certainly do not represent the norm. Insects, and particularly ants, comprise the majority of prey in both aerial and terrestrial pitchers.
Mutualism with mammals
Nepenthes rajah has evolved a mutualistic relationship with mountain treeshrews (Tupaia montana) in order to collect their droppings. The inside of the reflexed lid exudes a sweet nectar. The distance from the pitcher mouth to the exudate is the same as the average body length of the mountain treeshrew. As it feeds, the treeshrew defecates, apparently as a method of marking its feeding territory. It is thought that in exchange for providing nectar, the faeces provide the plant with the majority of the nitrogen it requires.Chin, L., J.A. Moran & C. Clarke 2010. Trap geometry in three giant montane pitcher plant species from Borneo is a function of tree shrew body size. New Phytologist 186 (2): 461–470. Walker, M. 2010. Giant meat-eating plants prefer to eat tree shrew poo. BBC Earth News, March 10, 2010.Clarke, C., J.A. Moran & L. Chin 2010. Mutualism between tree shrews and pitcher plants: perspectives and avenues for future research. Plant Signaling & Behavior 5(10): 1187–1189. Clarke, C. & J.A. Moran 2011. Incorporating ecological context: a revised protocol for the preservation of Nepenthes pitcher plant specimens (Nepenthaceae). Blumea 56(3): 225–228. Davies, E. 2012. . BBC Nature Features, November 15, 2012. In N. lowii, N. macrophylla and N. rajah, the colour of the lower lid surface corresponds to visual sensitivity maxima of the mountain treeshrew in the green and blue wavebands, making the lid underside stand out against adjacent parts of the pitcher.Moran, J.A., C. Clarke, M. Greenwood & L. Chin 2012. Tuning of color contrast signals to visual sensitivity maxima of tree shrews by three Bornean highland Nepenthes species. Plant Signaling & Behavior 7(10): 1267–1270. Of the three species, N. rajah shows the tightest 'fit', particularly in the green waveband.
In 2011, it was reported that N. rajah has a similar mutualistic relationship with the summit rat (Rattus baluensis).Wells, K., M.B. Lakim, S. Schulz & M. Ayasse 2011. Pitchers of Nepenthes rajah collect faecal droppings from both diurnal and nocturnal small mammals and emit fruity odour. Journal of Tropical Ecology 27(4): 347–353. Greenwood, M., C. Clarke, C.C. Lee, A. Gunsalam & R.H. Clarke 2011. A unique resource mutualism between the giant Bornean pitcher plant, Nepenthes rajah, and members of a small mammal community. PLoS ONE 6(6): e21114. Whereas the mountain treeshrew visits pitchers during daylight hours, the summit rat is primarily active at night; this may be an example of resource partitioning. Daily scat deposition rates were found to be similar for both mammalian species.
Other interactions with animals
Pitcher infauna
Although Nepenthes are most famous for trapping and digesting animals, their pitchers play host to a large number of other organisms (known as infauna). These include fly and midge larvae, spiders (crab spiders such as Henriksenia labuanica), mites, ants, and even a species of crab, Geosesarma malayanum. The most common and conspicuous predators found in pitchers are mosquito larvae, which consume large numbers of other larvae during their development. Many of these animals are so specialised that they cannot survive anywhere else, and are referred to as nepenthebionts.Beaver 1979, pp. 1–10.
The complex relationships between these various organisms are not yet fully understood. The question of whether infaunal animals "steal" food from their hosts, or whether they are involved in a mutually beneficial (symbiotic) association has yet to be investigated experimentally and is the source of considerable debate. Clarke suggests that mutualism is a "likely situation", whereby "the infauna receives domicile, protection and food from the plant, while in return, the infauna helps to break down the prey, increase the rate of digestion and keep bacterial numbers low".
Species specific
As the size and shape of Nepenthes pitchers vary greatly between species, but little within a given taxon, it is not surprising that many infaunal organisms are specially adapted to life in only the traps of particular species. N. rajah is no exception, and in fact has two mosquito taxa named after it. Culex (Culiciomyia) rajah and Toxorhynchites (Toxorhynchites) rajah were described by Masuhisa Tsukamoto in 1989, based on larvae collected in pitchers of N. rajah on Mount Kinabalu three years earlier.Tsukamoto 1989, p. 216. The two species were found to live in association with larvae of Culex (Lophoceraomyia) jenseni, Uranotaenia (Pseudoficalbia) moultoni and an undescribed taxon, Tripteroides (Rachionotomyia) sp. No. 2. Concerning C. rajah, Tsukamoto noted that the "body surface of most larvae are covered in Vorticella-like protozoa".Tsukamoto 1989, p. 220.