Nepenthes Rajah (8)

''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.Clarke 1997, p. 123. ''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 a.s.l. 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. Hooker called it "one of the most striking vegetable productions hither-to discovered".Hooker 1859. Since being introduced into cultivation in 1881, ''Nepenthes rajah'' has always been a much sought-after species. For a long time, the plant was seldom seen in private collections due to its rarity, price, and specialised growing requirements. However, recent advances in tissue culture technology have resulted in prices falling dramatically, and ''N. rajah'' is now relatively widespread in cultivation.

''Nepenthes rajah'' is most famous for the giant urn-shaped traps it produces, which can grow up to 41 cm highHamilton, G. 2011. The Sabah Society. and 20 cm wide.McPherson, S.R. 2009. ''Pitcher Plants of the Old World''. 2 volumes. Redfern Natural History Productions, Poole. These are capable of holding 3.5 litres of water  and in excess of 2.5 litres of digestive fluid, making them probably the largest in the genus by volume. Another morphological feature of ''N. rajah'' is the peltate leaf attachment of the lamina and tendril, which is present in only a few other species.

''Nepenthes rajah'' traps vertebrates and even small mammals, with drowned rats having been observed in the pitcher-shaped traps.Phillipps 1988, p. 55. It is one of only three ''Nepenthes'' species documented as having caught mammalian prey in the wild, the others being '' N. rafflesiana'' and '' N. attenboroughii''. ''N. rajah'' is also known to occasionally trap small vertebrates such as frogs, lizards, and even birds, although these cases probably involve sick animals and certainly do not represent the norm. Insects, and particularly ants, comprise the staple prey in both aerial and terrestrial pitchers.

Although ''Nepenthes rajah'' is most famous for trapping and digesting animals, its pitchers are also host to a large number of other organisms, which are thought to form a mutually beneficial (symbiotic) association with the plant. Many of these animals are so specialised that they cannot survive anywhere else, and are referred to as nepenthebionts. ''N. rajah'' has two such mosquito taxa named after it: ''Culex rajah'' and ''Toxorhynchites rajah''.

Another key feature of ''N. rajah'' is the relative ease with which it is able to hybridise in the wild. Hybrids between it and all other ''Nepenthes'' species on Mount Kinabalu have been recorded. However, due to the slow-growing nature of ''N. rajah'', few hybrids involving the species have been artificially produced yet.

Etymology

Joseph Dalton Hooker described ''Nepenthes rajah'' in 1859, naming it in honour of Sir James Brooke, the first White Rajah of Sarawak.Kurata 1976, p. 61. In the past, the Latin name was written as ''Nepenthes Rajah'',Danser 1928, 38. since it derives from a proper noun. However, this capitalisation is considered incorrect today. 'Rajah Brooke's Pitcher Plant'Phillipps & Lamb 1996, p. 129. is an accurate, but seldom-used common name. ''N. rajah'' is also 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 referred to as the "King of ''Nepenthes''".Steiner 2002, p. 94.

Plant characteristics

''Nepenthes rajah'', like virtually all species in the genus, is a scrambling vine. The stem usually grows along the ground, but will attempt to climb whenever it comes into contact with an object that can support it. The stem is relatively thick (≤30 mm) and may reach up to 6 m in length, although it rarely exceeds 3 m. ''N. rajah'' does not produce runners as some other species in the genus, but older plants are known to form basal offshoots. This is especially common in plants from tissue culture, where numerous offshoots may form at a young age.

Leaves

Leaves are produced at regular intervals along the stem. They are connected to the stem by sheathed structures known as petioles. A long, narrow tendril emanates from the end of each leaf. At the tip of the tendril is a small bud which, when physiologically activated, develops into a functioning trap. Hence, the pitchers are modified leaves and not specialised flowers as is often believed. The green structure most similar to a normal leaf is specifically known as the lamina or leaf blade.

The leaves of ''N. rajah'' are very 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. This characteristic is more pronounced in ''N. rajah'' than in any other ''Nepenthes'' species, with the exception of '' N. clipeata''. However, it is not unique to these two taxa, as mature plants of many ''Nepenthes'' species display slightly peltate leaves. The tendrils are inserted ≤5 cm below the leaf apex and reach a length of approximately 50 cm. Three to five longitudinal veins run along each side of the lamina and pennate (branching) veins run towards the margin. The lamina is oblong to lanceolate-shaped, ≤80 cm long and ≤15 cm wide.

Pitchers

All ''Nepenthes'' pitchers share several basic characteristics. Traps consist of the main pitcher cup, which is covered by an operculum or lid that prevents rainwater from entering the pitcher and displacing or diluting its contents. A reflexed ring of hardened tissue, known as the peristome, surrounds the entrance to the pitcher (only the aerial pitchers of '' N. inermis'' lack a peristome). A pair of fringed wings run down the front of lower traps and these presumably serve to guide terrestrial insects into the pitchers' mouth. Accordingly, the wings are greatly reduced or completely lacking in aerial pitchers, for which flying insects constitute the majority of prey items.

''Nepenthes rajah'', like most species in the genus, produces two distinct types of traps. "Lower" or "terrestrial" pitchers are the most common. These are very large, richly coloured, and ovoid in shape. In lower pitchers, the tendril attachment occurs at the front of the pitcher cup relative to the peristome and wings. Exceptional specimens may be more than 40 cm in length and hold 3.5 litres of water  and in excess of 2.5 litres of digestive fluid, although most do not exceed 200 ml.Clarke 2001b, p. 7.

The largest recorded pitcher of ''N. rajah'', measuring 41 cm, was found on March 26, 2011, during a trip to Mesilau organised by The Sabah Society. The trap was discovered next to a steep sidepath of the Mesilau nature trail and was measured by Alex Lamb, son of Anthea Phillipps and Anthony Lamb, who were also on the trip. It was collected for preservation at Mesilau Headquarters. Another trap measuring 40 cm was spotted on the same day. The previous record for a ''N. rajah'' pitcher was 38 cm.

The lower pitchers of ''N. rajah'' are probably the largest in the genus by volume, rivaled only by those of '' N. merrilliana'', '' N. truncata'' and the giant form of '' N. rafflesiana''. These traps rest on the ground and are often reclined, leaning against surrounding objects for support. They are usually red to purple on the outside, whilst the inside surfaces are lime green to purple. This contrasts with all other parts of the plant, which are yellow-green. The lower pitchers of ''N. rajah'' are unmistakable and for this reason it is easy to distinguish it from all other Bornean ''Nepenthes'' species.

Mature plants may also produce "upper" or "aerial" pitchers, which are much smaller, funnel-shaped, and usually more colourful than the lowers. The tendril attachment in upper pitchers is normally present at the rear of the pitcher cup. True upper pitchers are seldom seen, as the stems of ''N. rajah'' rarely attain lengths greater than a few metres before dying off and being replaced by off-shoots from the main rootstock.

Upper and lower pitchers differ significantly in morphology, as they are specialised for attracting and capturing different prey. Pitchers that do not fall directly into either category are simply known as "intermediate" pitchers.

The peristome of ''N. rajah'' has a highly distinctive scalloped edge and is greatly expanded, forming an attractive red lip around the trap's mouth. A series of raised protrusions, known as 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 in this species.Bauer, U., C.J. Clemente, T. Renner & W. Federle 2012. Form follows function: morphological diversification and alternative trapping strategies in carnivorous ''Nepenthes'' pitcher plants. ''Journal of Evolutionary Biology'' 25(1): 90–102. Two fringed wings run from the tendril attachment to the lower edge of the peristome.

The huge, vaulted lid of ''N. rajah'', the largest in the genus, is another distinguishing characteristic of this species. It is ovate to oblong in shape and has a distinct keel running down the middle, with two prominent lateral veins. The spur at the back of the lid is approximately 20 mm long and unbranched.Clarke 1997, p. 122.

''Nepenthes rajah'' is noted for having very large nectar- secreting glands covering its pitchers. These are quite different from those of any other ''Nepenthes'' and are easily recognisable. The inner surface of the pitcher, in particular, is wholly glandular, with 300 to 800 glands/cm².

Flowers

''Nepenthes 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 80 cm, and sometimes even 120 cm tall. The individual flowers of ''N. rajah'' are produced on partial peduncles (twin stalks) and so the inflorescence is called a raceme (as opposed to a panicle for multi-flowered bunches). The flowers are reported to give off a strong sugary smell and are brownish-yellow in colour. Sepals are elliptic to oblong and ≤8 mm 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 10 to 20 mm long (see image). A study of 300 pollen samples taken from a herbarium specimen (''J.H.Adam 2443'', collected at an altitude of 1930–2320 m) found the mean pollen diameter to be 34.7 μm ( SE = 0.3; CV = 7.0%).

Other characteristics

The root system of ''N. rajah'' is notably extensive, although it is relatively shallow as in most ''Nepenthes'' species.

All parts of the plant are covered in long, white hairs when young, but mature plants are virtually glabrous (lacking hair). This covering of hair is known as the indumentum.

The colour of herbarium specimens is dark-brown in varying hues (see image).

Little variation has been observed within natural populations of ''Nepenthes rajah'' and, consequently, no forms or varieties have been described. Furthermore, ''N. rajah'' has no true nomenclatural synonyms,Clarke 1997, p. 120. unlike many other ''Nepenthes'' species, which exhibit greater variability.

Carnivory

''Nepenthes 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, the discovery of a drowned mountain treeshrew (''Tupaia montana'') in a ''N. rajah'' pitcher was reported.

''Nepenthes rajah'' is also known to occasionally trap 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.Clarke 1997, p. 33. Insects, and particularly ants, comprise the majority of prey in both aerial and terrestrial pitchers. Other arthropods, such as centipedes, also fall prey to ''N. rajah''.

''Nepenthes rafflesiana'' is one of the few other ''Nepenthes'' species reliably documented as having caught mammalian prey in its natural habitat. In Brunei, frogs, geckos and skinks have been found in the pitchers of this species. The remains of mice have also been reported. On September 29, 2006, at the Jardin botanique de Lyon in France, a cultivated '' N. truncata'' was photographed containing the decomposing corpse of a mouse.

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. These proportions also hold true for '' N. lowii'' and '' N. macrophylla''. 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 ''N. rajah'' with the majority of the nitrogen it requires.Walker, M. 2010
Giant meat-eating plants prefer to eat tree shrew poo
''BBC Earth News'', March 10, 2010. 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 also play host to a large number of other organisms (known as infauna). These include fly and midge larvae, spiders (most notably the crab spider '' Misumenops nepenthicola''), 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.

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. 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. At present, nothing is known of this species with regards to its adult biology, habitat, or medical importance as a vector of diseases. The same is true for ''T. rajah''; nothing is known of its biology except that adults are not haematophagous.

Another species, ''Culex shebbearei'', has also been recorded as an infaunal organism of ''N. rajah'' in the past. The original 1931 record by F. W. Edwards is based on a collection by H. M. Pendlebury in 1929 from a plant growing on Mount Kinabalu. However, Tsukamoto notes that in light of new information on these species, "it seems more likely to conclude that the species 'C. rajah''is a new species which has been misidentitied as ''C. shebbearei'' for a long time, rather than to think that both ''C. shebbearei'' and ''C. rajah'' n. sp. are living in pitchers of ''Nepenthes rajah'' on Mt. Kinabalu".

Pests

Not all interactions between ''Nepenthes'' and fauna are beneficial to the plant. ''Nepenthes rajah'' is sometimes attacked by insects which feed on its leaves and damage substantial portions of the lamina. Also, monkeys and tarsiers are known to occasionally rip pitchers open to feed on their contents.

History and popularity

Due to its size, unusual morphology and striking colouration, ''N. rajah'' has always been a very popular and highly sought-after insectivorous plant. However, despite its popularity amongst pitcher plant enthusiasts, ''N. rajah'' remains a little-known species outside the field of carnivorous plants. Due to its specialised growing requirements, it is not a suitable candidate for a houseplant and, as such, is only cultivated by a relatively small number of hobbyists and professional growers worldwide. This being the case, ''N. rajah'' is nonetheless probably the most famous of all pitcher plants. Its reputation for producing some of the most magnificent pitchers in the genus dates back to the late 19th century.

''Nepenthes rajah'' was first collected by Hugh Low on Mount Kinabalu in 1858. It was described the following year by Joseph Dalton Hooker, who named it after James Brooke, the first White Rajah of Sarawak. The description was published in ''The Transactions of the Linnean Society of London'':

''Nepenthes Rajah'', H. f. (Frutex, 4-pedalis, ''Low''). Foliis maximis 2-pedalibus, oblongo-lanceolatis petiolo costaque crassissimis, ascidiis giganteis (cum operculo l-2-pedalibus) ampullaceis ore contracto, stipite folio peltatim affixo, annulo maximo lato everso crebre lamellato, operculo amplissimo ovato-cordato, ascidium totum æquante.—(''Tab.'' LXXII.)

''Hab.''—Borneo, north coast, on Kina Balu, alt. 5,000 feet (''Low''). This wonderful plant is certainly one of the most striking vegetable productions hitherto discovered, and, in this respect, is worthy of taking place side by side with the ''Rafflesia Arnoldii''. It hence bears the title of my friend Rajah Brooke, of whose services, in its native place, it may be commemorative among botanists. . . . I have only two specimens of leaves and pitchers, both quite similar, but one
twice as large as the other. Of these, the leaf of the larger is 18 inches long, exclusive of the petioles, which is as thick as the thumb and 7–8 broad, very coriaceous and glabrous, with indistinct nerves. The stipes of the pitcher is given off below the apex of the leaf, is 20 inches long, and as thick as the finger. The broad ampullaceous pitcher is 6 inches in diameter, and 12 long: it has two fimbriated wings in front, is covered with long rusty hairs above, is wholly studded with glands within, and the broad annulus is everted, and 1–1 inch in diameter. Operculum shortly stipitate, 10 inches long and 8 broad.

The inflorescence is hardly in proportion. Male raceme, 30 inches long, of which 20 are occupied by the flowers; upper part and flowers clothed with short rusty pubescence. Peduncles slender, simple or bifid. Fruiting raceme stout. Peduncles 1 inches long, often bifid. Capsule, inch long, broad, rather turgid, densely covered with rusty tomentum.

Spenser St. John wrote the following account of his encounter with ''N. rajah'' on Mount Kinabalu in ''Life in the Forests of the Far East'' published in 1862:

Another steep climb of 800 feet brought us to the Marei Parei spur, to the spot where the ground was covered with the magnificent pitcher-plants, of which we had come in search. This one has been called the ''Nepenthes Rajah'', and is a plant about four feet in length, with broad leaves stretching on every side, having the great pitchers resting on the ground in a circle about it. Their shape and size are remarkable. I will give the measurement of one, to indicate the form: the length along the back nearly fourteen inches; from the base to the top of the column in front, five inches; and its lid a foot long by fourteen inches broad, and of an oval shape. Its mouth was surrounded by a plaited pile, which near the column was two inches broad, lessening in its narrowest part to three-quarters of an inch. The plaited pile of the mouth was also undulating in broad waves. Near the stem the pitcher is four inches deep, so that the mouth is situated upon it in a triangular manner. The colour of an old chalice is a deep purple, but that of the others is generally mauve outside, very dark indeed in the lower part, though lighter towards the rim; the inside is of the same colour, but has a kind of glazed and shiny appearance. The lid is mauve in the centre, shading to green at the edges. The stems of the female flowers we found always a foot shorter than those of the male, and the former were far less numerous than the latter. It is indeed one of the most astonishing productions of nature.

..The pitchers, as I have before observed, rest on the ground in a circle, and the young plants have cups of the same form as those of the old ones. While the men were cooking their rice, we sat before the tent enjoying our chocolate and observing one of our followers carrying water in a splendid specimen of the ''Nepenthes Rajah'', desired him to bring it to us, and found that it held exactly four pint bottles. It was 19 inches in circumference. We afterwards saw others apparently much larger, and Mr. Low, while wandering in search of flowers, came upon one in which was a drowned rat.

''Nepenthes rajah'' was first collected for the Veitch Nurseries by Frederick William Burbidge in 1878, during his second trip to Borneo. Shortly after being introduced into cultivation in 1881, ''N. rajah'' proved very popular among wealthy Victorian horticulturalists and became a much sought-after species. A note in ''The Gardeners' Chronicle'' of 1881 mentions the Veitch plant as follows: "''N. rajah'' at present is only a young Rajah, what it will become was lately illustrated in our columns...". A year later, young ''N. rajah'' plants were displayed at the Royal Horticultural Society's annual show for the first time.Phillipps & Lamb 1996, p. 22. The specimen exhibited at the show by the Veitch Nurseries, the first of this species to be cultivated in Europe, won a first class certificate. In Veitch's catalogue for 1889, ''N. rajah'' was priced at £2.2 s per plant. During this time, interest in ''Nepenthes'' had reached its peak. '' The Garden'' reported that ''Nepenthes'' were being propagated by the thousands to keep up with European demand.

However, dwindling interest in ''Nepenthes'' at the turn of the century saw the demise of the Veitch Nurseries and consequently the loss of several species and hybrids in cultivation, including '' N. northiana'' and ''N. rajah''. By 1905, the final ''N. rajah'' specimens from the Veitch nurseries were gone, as the cultural requirements of the plants proved too difficult to reproduce. The last surviving ''N. rajah'' in cultivation at this time was located at the National Botanic Gardens at Glasnevin in Ireland, however this soon perished also. It would be many years before ''N. rajah'' was reintroduced into cultivation.

Recent popularity

In recent years there has been renewed interest in ''Nepenthes'' worldwide. Much of the plants' current popularity can probably be attributed to Shigeo Kurata, whose book ''Nepenthes of Mount Kinabalu'' (1976), which featured the best colour photography of ''Nepenthes'' to date, did much to bring attention to these unusual plants.

Not surprisingly, ''N. rajah'' is a relatively well known plant in Malaysia, especially its native Sabah. The species is often used to promote Sabah, and specifically Kinabalu National Park, as a tourist destination, and features prominently on postcards from the region. ''Nepenthes rajah'' has appeared on the covers of several popular ''Nepenthes'' publications, including ''Nepenthes of Mount Kinabalu'' ( Kurata, 1976) and ''Nepenthes of Borneo'' (Clarke, 1997), both published in Kota Kinabalu, Malaysia. On April 6, 1996, Malaysia issued a series of four postage stamps depicting some of its more famous ''Nepenthes'' species. Two 30 ¢ stamps, featuring '' N. macfarlanei'' and '' N. sanguinea'', as well as two 50¢ stamps, depicting '' N. lowii'' and ''N. rajah'', were released. The ''N. rajah'' stamp has been assigned a unique identification number in two popular stamp numbering systems: Scott #580 and Yvert #600. Curiously, the peltate leaf attachment that is so characteristic of this species is not shown. ''Nepenthes rajah'' was featured in the first episode of ''Kingdom of Plants 3D'', a natural history documentary series presented by David Attenborough.

Classification

''Nepenthes rajah'' is not generally considered to be closely related to any other species, due to its unusual pitcher and leaf morphology. However, several attempts have been made to deduce natural groupings within the genus ''Nepenthes'', which have grouped ''N. rajah'' with other species thought to share certain traits with it.

The ''Nepenthes'' were first split up in 1873, when Hooker published his monograph on the genus, titled "Nepenthaceae". Hooker distinguished '' N. pervillei'' from all other taxa based on its seeds, which lack the appendages typical of most ''Nepenthes''. He placed it in the monotypic subgenus ''Anourosperma''. All other species were subsumed in the second subgenus, ''Eunepenthes''.

A second attempt to establish a natural subdivision within the genus was made in 1895 by Günther Beck von Mannagetta und Lerchenau in " Die Gattung ''Nepenthes''". Beck kept the two subgenera created by Hooker, but divided ''Eunepenthes'' into three subgroups: ''Retiferae'', ''Apruinosae'' and ''Pruinosae''. ''Nepenthes rajah'' formed part of the ''Apruinosae '' (Latin: pl. of ''apruinosa'': not frosted).

''Nepenthes'' taxonomy was once again revised in 1908 by John Muirhead Macfarlane in his own monograph, "Nepenthaceae". Oddly, Macfarlane did not name the groups he distinguished. His revision is not generally considered to be a natural division of the genus.

In 1928, B. H. Danser published his seminal monograph, "The Nepenthaceae of the Netherlands Indies", in which he divided ''Nepenthes'' into six clades, based on observations of herbarium material. The clades were: the ''Vulgatae'', ''Montanae'', ''Nobiles'', ''Regiae'', ''Insignes'' and ''Urceolatae''. Danser placed ''N. rajah'' in the ''Regiae'' (Latin: pl. of ''rēgia'': royal). The ''Regiae'' clade as proposed by Danser is shown in the adjacent table.

Most of the species in this clade are large plants with petiolate leaves, an indumentum of coarse reddish-brown hairs, raceme-like inflorescence, and funnel-shaped (infundibulate) upper pitchers. All bear a characteristic appendage on the lower surface of the lid near the apex. With the exception of ''N. lowii'', the ''Regiae'' all have a mostly flattened or expanded peristome. The majority of species comprising ''Regiae'' are endemic to Borneo. Based on current understanding of the genus, ''Regiae'' appears to reflect the relationships of its members quite well, although the same cannot be said for the other clades. Despite this, Danser's classification was undoubtedly a great improvement on previous attempts.

The taxonomical work of Danser (1928) was revised by Hermann Harms in 1936. Harms divided ''Nepenthes'' into three subgenera: ''Anurosperma'' Hooker.f. (1873), ''Eunepenthes'' Hooker.f. (1873) and ''Mesonepenthes'' Harms (1936) (Latin: ''meso'': middle; "middle" ''Nepenthes''). The ''Nepenthes'' species found in the subgenera ''Anurosperma'' and ''Mesonepenthes'' differ from those in the ''Vulgatae'', where Danser had placed them. Harms included ''N. rajah'' in the subgenus ''Eunepenthes'' together with the great majority of other ''Nepenthes''; ''Anurosperma'' was a monotypic subgenus, while ''Mesonepenthes'' contained only three species. He also created an additional clade, the ''Distillatoriae'' (after '' N. distillatoria'').

In his 1976 book, ''Nepenthes of Mount Kinabalu'', Shigeo Kurata presented detailed photographs of lid nectar glands and the digestive glands of the trap interior. He divided the latter into the "lower", "upper" and "middle" parts.

Biochemical analysis

More recently, biochemical analysis has been used as a means to determine cladistical relationships between ''Nepenthes'' species. In 1975, David E. Fairbrothers ''et al.'' first suggested a link between chemical properties and certain morphological groupings, based on the theory that morphologically similar plants produce chemical constituents with similar therapeutic effects.

In 2002, phytochemical screening and analytical chromatography were used to study the presence of phenolic compounds and leucoanthocyanins in several naturally occurring hybrids and their putative parental species (including ''N. rajah'') from Sabah and Sarawak. The research was based on leaf material from nine dry herbarium specimens. Eight spots containing phenolic acids, flavonols, flavones, leucoanthocyanins and 'unknown flavonoid' 1 and 3 were identified from chromatographic profiles. The distributions of these in the hybrid ''N. × alisaputrana'' and its putative parental species ''N. rajah'' and ''N. burbidgeae'' are shown in the adjacent table. A specimen of ''N. × alisaputrana'' grown from tissue culture (''in vitro'') was also tested.

Phenolic and ellagic acids were undetected in ''N. rajah'', while concentrations of kaempferol were found to be very weak. Chromatographic patterns of the ''N. × alisaputrana'' samples studied showed complementation of its putative parental species.

Myricetin was found to be absent from all studied taxa. This agrees with the findings of previous authors ( R. M. Som in 1988; M. Jay and P. Lebreton in 1972) and suggests that the absence of a widely distributed compound like myricetin among the ''Nepenthes'' examined might provide "additional diagnostic information for these six species".

Several proteins and nucleotides of ''N. rajah'' have been either partially or completely sequenced. These are as follows:

translocated tRNA-Lys (trnK) pseudogene (DQ007139)

trnK gene & maturase K (matK) gene (AF315879)
ref name=Meimberg>Meimberg ''et al.'' 2001

trnK gene & maturase K (matK) gene (AF315880)
ref name=Meimberg/>

maturase K (AAK56010)
ref name=Meimberg/>

maturase K (AAK56011)
ref name=Meimberg/>

Related species

In 1998, a striking new species of ''Nepenthes'' was discovered in the Philippines by Andreas Wistuba. Temporarily dubbed ''N.'' sp. Palawan 1, it bears a close resemblance to ''N. rajah'' in terms of pitcher and leaf morpholog

https://web.archive.org/web/20070311135054/http://www.heliamphora.de/shop/images/nsppalawan3.jp

In 2007, the species was described by Wistuba and Joachim Nerz as '' N. mantalingajanensis''.

Ecology

Kinabalu

''Nepenthes rajah'' has a very localised distribution, being restricted to Mount Kinabalu and neighbouring Mount Tambuyukon, both located in Kinabalu National Park, Sabah, Malaysian Borneo.Clarke 1997, p. 123. Mount Kinabalu is a massive granitic dome structure that is geologically young and formed from the intrusion and uplift of a granitic batholith. At 4095.2 m, it is by far the tallest mountain on the island of Borneo and one of the highest peaks in Southeast Asia. The lower slopes of the mountain are mainly composed of sandstone and shale, transformed from marine sand and mud about 35 million years ago. Intrusive ultramafic ( serpentine) rock was uplifted with the core of the batholith and forms a collar around the mountain. It is on these ultramafic soils that the flora of Mount Kinabalu exhibits the greatest levels of endemicity and many of the area's rarest species can be found here.

Substrate

''Nepenthes rajah'' seems to grow exclusively on serpentine soils containing high concentrations of nickel and chromium, which are toxic to many plant species. Its tolerance of these, therefore, means that it can grow in an ecological niche where it faces less competition for space and nutrients. The root systems of '' N. × alisaputrana'' and '' N. villosa'' are also known to be resistant to the heavy metals present in serpentine substrates. These soils are also rich in magnesium and are slightly alkaline as a result. They often form a relatively thin layer over a base of ultramafic rock and are thus known as ultramafic soils. Ultramafic soils are thought to cover approximately 16% of Kinabalu National Park. These soils have high levels of endemicity in many taxonomic groups, not least the ''Nepenthes''. Four species in the genus, including ''N. rajah'', can only be found within the boundaries of the park.

''Nepenthes rajah'' usually grows in open, grassy clearings on old land slips and flat ridge tops, particularly in areas of seeping ground water, where the soil is loose and permanently moist. Although these sites can receive very high rainfall, excess water drains away quickly, preventing the soil from becoming waterlogged. ''N. rajah'' can often be found growing in grassy undergrowth, especially among sedges.

Climate

''Nepenthes rajah'' has an altitudinal distribution of 1500–2650 m a.s.l. and is thus considered an (ultra) highland or Upper Montane plant. In the upper limit of its range, night-time temperatures may approach freezing and day-time maxima rarely exceed 25 °C. Due to the night-time temperature drop, relative air humidity increases significantly, rising from 65 to 75% to over 95%. Vegetation at this height is very stunted and slow-growing due to the extreme environmental conditions that prevail. Plants are often subjected to fierce winds and driving rain, as well as exposure to intense direct sunlight. The relatively open vegetation of the upper montane forest also experiences greater fluctuations in temperature and humidity compared with lower altitudes. These changes are largely governed by the extent of cloud cover. In the absence of clouds, temperatures rise rapidly, humidity drops, and light levels may be very high. When cloud cover returns, temperatures and light levels fall, while humidity levels increase. Average annual precipitation in this region is around 3000 mm.

Conservation status

Endangered species

''Nepenthes rajah'' is classified as Endangered (EN – B1+2e) on the IUCN Red List of Threatened Species. It is also listed on Schedule I, Part II of the Wildlife Conservation Enactment (WCE) 1997 and CITES Appendix I,  which prohibits commercial international trade in plants collected from the wild. However, due to its popularity among collectors, many plants have been removed from the wild illegally, even though the species' distribution lies entirely within the bounds of Kinabalu Park. This led to some populations being severely depleted by over-collection in the 1970s and eventually resulted in the species' inclusion in CITES Appendix I in 1981. Together with '' N. khasiana'', it is one of only two species in the genus to feature on this list; all other ''Nepenthes'' species are covered by Appendix II.

This being the case, however, the short-term future of ''N. rajah'' seems to be relatively secure and it would perhaps be more accurately classified as Vulnerable (VU) or, taking into account protected populations in National Parks, Lower Risk conservation dependent (LR (cd)). This agrees with the conservation status of ''N. rajah'' according to the World Conservation Monitoring Centre (WCMC), under which it is also considered Vulnerable. Furthermore, the species was originally treated as Vulnerable (V) by the IUCN prior to the introduction of the 1994 threat categories.

Although ''N. rajah'' has a restricted distribution and is often quoted as a plant in peril, it is not rare in the areas where it does grow and most populations are now off-limits to visitors and lie in remote parts of Kinabalu National Park. Furthermore, ''N. rajah'' has a distinctive leaf shape making it difficult to illegally ship abroad even if the pitchers are removed, as an informed customs official should be able to identify it.

The recent advent of artificial tissue culture, or more specifically ''in vitro'', technology in Europe and the United States has meant that plants can be produced in large numbers and sold at relatively low prices (~US$20–$30 in the case of ''N. rajah''). ''In vitro'' propagation refers to production of whole plants from cell cultures derived from explants (generally seeds). This technology has, to a large extent, removed the incentive for collectors to travel to Sabah to collect the plant illegally, and demand for wild-collected plants has fallen considerably in recent years.

Rob Cantley, a prominent conservationist and artificial propagator of ''Nepenthes'' plants, assesses the current status of plants in the wild as follows:

This species grows in at least 2 distinct sub-populations, both of which are well protected by Sabah National Parks Authority. One of the populations grows in an area public access to which is strictly prohibited without permit. However, there has been a decline in population of mature individuals in the better known and less patrolled site. This is largely due to damage to habitat and plants by careless visitors rather than organised collection of plants. Nepenthes rajah has become common in cultivation in recent years as a result of the availability of inexpensive clones from tissue culture. I believe that these days commercial collection of this species from the wild is negligible.

This being the case, however, it appears that the genetic variability of cultivated ''N. rajah'' plants is very small, as all commercially available tissue-cultured plants are thought to belong to just four clones originating from the Royal Botanic Gardens, Kew in London, England.

However, illegal collection is not the only threat facing plants in the wild. The El Niño climatic phenomenon of 1997/98 had a catastrophic effect on the ''Nepenthes'' species on Mount Kinabalu. The dry period that followed severely depleted some natural populations. Forest fires broke out in 9 locations in Kinabalu Park, covering a total area of 25 square kilometres and generating large amounts of smog. During the El Niño period, many plants were temporarily transferred to the park nursery to save at least some individuals. These were later replanted in the "''Nepenthes'' Garden" in Mesilau (see below). In spite of this, ''N. rajah'' was one of the less affected species and relatively few plants perished as a result. Since then, Ansow Gunsalam has established a nursery close to the Mesilau Lodge at the base of Kinabalu Park to protect the endangered species of that area, including ''N. rajah''.

Restricted distribution

The newly opened Mesilau Nature Resort, which lies near the golf course behind the village of Kundasang, is now the only place where regular visitors can hope to see this species in its natural habitat.Clarke 2001b, p. 38. Here, several dozen ''N. rajah'' plants grow near the top of a steep landslide. Both young and mature plants are present, some with sizable pitchers that may occasionally exceed 40 cm in height (see image). Daily guided tours are organised to the "''Nepenthes'' Garden" where these plants are located. The "''Nepenthes rajah'' Nature Trail" is subject to a fee and operates daily from 9:00 am to 4:00 pm. Almost all other natural populations of this species occur in remote parts of Kinabalu National Park, which are off-limits to tourists. Visitors to the park can also see ''N. rajah'' on display in the nursery adjoining the "Mountain Garden" at Kinabalu Park Headquarters.

Other known localities of wild ''N. rajah'' populations include the Marai Parai plateau, Mesilau East River near Mesilau Cave, the Upper Kolopis River, and the eastern slope of Mount Tambuyukon. On Pig Hill, ''N. rajah'' grows at 1950–2320 m and is sympatric with '' N. burbidgeae'', '' N. tentaculata'', and the natural hybrid '' N. × alisaputrana''.Thong, J. 2006. ''Victorian Carnivorous Plant Society Journal'' 82: 6–12.

Natural hybrids

''Nepenthes rajah'' is known to hybridise with several other species with which it is sympatric. It seems to flower at any time of year and for this reason it hybridises relatively easily. Charles Clarke also notes that "''N. rajah'', more than any other species, appears to have been successful in having its pollen transported over considerable distances. Consequently, a number of putative ''N. rajah'' hybrids exist without the parent plant growing nearby". However, it appears that the limit as to how far pollen can be transported is approximately 10 km. Hybrids between ''N. rajah'' and all other ''Nepenthes'' species on Mount Kinabalu have been recorded.A rare find: ''N. rajah'' nat. hybrid
Flora Nepenthaceae. Due to the slow-growing nature of ''N. rajah'', few hybrids involving it have been artificially produced yet.

At present, the following natural hybrids are known:

* '' N. burbidgeae'' × ''N. rajah'' N. × alisaputrana'' J. H. Adam">J.H.Adam & C. C. Wilcock">Wilcock