- While upon the subject of plants I may here mention a few of the more striking vegetable productions of Borneo. The wonderful Pitcher-plants, forming the genus Nepenthes of botanists, here reach their greatest development. Every mountain-top abounds with them, running along the ground, or climbing over shrubs and stunted trees; their elegant pitchers hanging in every direction. Some of these are long and slender, resembling in form the beautiful Philippine lace-sponge (Euplectella), which has now become so common; others are broad and short. Their colours are green, variously tinted and mottled with red or purple. The finest yet known were obtained on the summit of Kini-balou, in North-west Borneo. One of the broad sort, Nepenthes rajah, will hold two quarts of water in its pitcher. Another, Nepenthes Edwardsiania, has a narrow pitcher twenty inches long; while the plant itself grows to a length of twenty feet.
- Alfred Russel Wallace, 1869. The Malay Archipelago, Volume I
- This very striking species has never been confounded with any other.
- The specific epithet rajah means "King" in Malay and was named after Sir James Brooke, the Rajah of Sarawak. This large and splendid Nepenthes distinguishes itself by its peltate-tipped leaf and large pitcher with a deeply vaulted lid which is always larger than the pitcher mouth, N. rajah is rather fond of wet places like swamps or the surroundings of a water fall. Marai Parai plateau is well known as a habitat of this species. Recently other places mentioned above [the Mesilau-East River (near Mesilau Cave), the Upper Kolopis River and eastern slope of Mt. Tambuyukon] are recorded as new habitats.
- This spectacular species is the most famous of all pitcher plants. Known to catch rats, frogs and lizards as well as insects, the huge pitchers of N. rajah are unmistakable. This species was named in honour of Sir James Brooke, one of the White Rajahs of Sarawak's past. It grows only on Mount Kinabalu and Mount Tambuyukon in Sabah, though it is not rare in this area. Legend has it that this species grows only in the spray zones around waterfalls, on ultramafic soils. Although it is true that it grows on ultramafic soils, it is certainly not found in the spray zones of waterfalls, but grows in open, grassy areas within its altitudinal distribution. Generally these areas are land slips or flat ridge tops, where the soil is loose. Although rainfall may be very high in these places, excess water seems to drain away quickly, and the plants are most common at seepages which are less prone to drying out.
The stems of N. rajah tend to be decumbent rather than climbing. The leaves are distinctive, as the tendril is inserted about 2 cm from the apex. Although this characteristic is more pronounced in N. rajah and N. clipeata than in other species, it is not necessarily exclusive, as mature plants of many species have slightly peltate leaves. The lower pitchers are tub-shaped and do not sit upright, but lean back against other objects. Up to one litre of fluid may be contained in a pitcher. The peristome is wide and distinctly scalloped. The lid is vaulted and very large relative to the rest of the pitcher. The exterior parts of the pitcher are scarlet to purple, while the inside is yellow to purple. All other parts are yellow-green.
Upper and intermediate pitchers are rarely produced, but are smaller, less brightly coloured, and more funnel-shaped than the lower pitchers. The flowers are usually brownish-yellow in colour and, like those of many Nepenthes, have a strong sugary smell. This species seems to flower at any time of the year and hybrids between it and all other Nepenthes species on Mount Kinabalu, except N. lowii, have been recorded. There is no noticeable variation within N. rajah, and no forms or varieties have been described.
- When Hooker described this species, also discovered by Hugh Low on Mt. Kinabalu, he wrote, "This wonderful plant is certainly one of the most striking vegetable productions hitherto discovered...", and it remains so to this day. Also found on Mt. Tambuyukon, N. rajah grows along the ground as a scrambler. The large leaves are blunt and truncated, and the tendril originates from the middle underside. The enormous pitchers are oval-shaped, almost woody in texture, red to purple in color, with a large, gapping, oblique mouth. The thick, fluted peristome is blood red. The interior of the tublike traps is pale green to pink and has no waxy zone, being entirely covered with large digestive glands. The giant lid is vaulted, red above and lime green below. The pitchers can be over a foot in length, and can hold over two quarts of digestive juices, but there have been specimens known to hold four quarts. The flower spikes can also be impressive, standing as tall as four feet. Climbing stems are rare.
N. rajah is the only pitcher plant truly documented as having caught rats. It is believed the mammals were in search of water when they fell in and drowned.
- The most famous of all pitcher plants is the giant N. rajah, found only on Mount Kinabalu and neighbouring Mount Tambuyukon in Sabah. The pitchers are unmistakable in appearance, being large (≤35 cm high) and ovoid in shape with a huge, vaulted lid. The peristome is expanded and scalloped at the outer edge, while the inner margin is lined with short, sharp teeth. The pitchers rest on the ground and are often reclined, leaning against surrounding objects for support. The tendril joins the leaf blade just below the tip, which is a distinctive feature. The pitchers are usually dark purple in colour while the peristome ranges from red to purple.
Nepenthes rajah grows in open, grassy vegetation in sites which are permanently moist. It always grows terrestrially in serpentine soils. There are no habitats of this type along the main summit trail of Mount Kinabalu, so it is not seen by most visitors. However, a small population persists near the newly opened Mesilau Resort, and interested visitors are sometimes taken to see these plants by the staff of Kinabalu Park. Some populations of N. rajah were seriously depleted by over collection in the 1970's. However, most populations are now off-limits to visitors and lie in remote parts of Kinabalu Park. Artificial propagation of plants in Western countries has helped reduce demand for plants collected from the wild, so the long term outlook for the survival of N. rajah in the wild is comparatively good.
- Sir Joseph Hooker (1873) wrote enthusiastically of this plant: "This wonderful plant is certainly one of the most striking vegetable productions hither-to 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 service in its native place it may be commemorative among botanists." As rajah means ruler or king, it has been called by some the "King of Nepenthes". Many stories are woven around this plant. It probably has the largest pitchers, and both Phillipps and Lamb (1996) and St. John (1862) observed drowned rats in a pitcher with a capacity of more than two litres. This plant grows only in Sabah, on Mount Kinabalu at 1500-2600 m and Mount Tambuyukon, and seems to prefer humid zones and land slips. There are many hybrids of N. rajah, perhaps because this species flowers at any time of the year, and, with the exception N. lowii, all species on Mount Kinabalu seem to have hybridised with N. rajah. We found these huge plants on the slopes of the Mesilau Valley northeast of Kinabalu Park Headquarters, a grassy region near a waterfall, therefore providing quite a humid microclimate.
- 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.