Nepenthes L. (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Nepenthes L.

Protologue: Sp. pl.: 955 (1753); Gen. pl. ed. 5: 409 (1754).

Family: Nepenthaceae

Chromosome number: <4>x= 5 (10?);N. rafflesiana: 2n= 80

• Nepenthes ampullaria Jack, Comp. Bot. Mag. 1: 271 (1835), synonym: N. ampullacea H. Low (1848).

• Nepenthes rafflesiana Jack, Comp. Bot. Mag. 1: 270 (1835), synonyms: N. raflesea Hort. (1869), N. sanderiana Burb. (1904), N. hemsleyana Macfarl. (1908).

• General: pitcher plant, tropical pitcher plant, monkey pot (En)
• Indonesia: daun kendi (Moluccas), ketakong (Bangka), paku sorog (Sundanese)
• Malaysia: periuk kera, periuk monyet, periuk kerengga.

• N. ampullaria : Indonesia: kantong teko (general), ketakong betul (Bangka), katidieng boruak (West Sumatra)
• Malaysia: akar periuk kera, periuk kera, akar cerek-cerek
• Thailand: cho mokaeng, mokaeng khaang (Pattani), blaa-ngo-kue-ko (Malay-Pattani).

• N. rafflesiana : Indonesia: periuk kera (Lingga), ketakong menjang (Bangka).

Nepenthes is believed to have originated in the western Indian Ocean region and comprises about 87 species, mostly in Malesia (Malaysia, Singapore, Brunei, Indonesia, the Philippines, Papua New Guinea), with most species found in Borneo and Sumatra. It is not known from the Lesser Sunda Islands and the northern tip of Sumatra. Some outlying species occur in Madagascar, the Seychelles, Sri Lanka, India, Indo-China, the Solomon Islands, New Caledonia and Australia. N. ampullaria is distributed in Thailand, Peninsular Malaysia, Sumatra, Borneo and New Guinea. N. rafflesiana is found in Peninsular Malaysia, Sumatra and Borneo. It is one of the most abundant Nepenthes spp. in northern Borneo, abundant in the Riau Archipelago (Indonesia) and in Singapore, but rare in mainland Sumatra and Peninsular Malaysia.

Although the major use of Nepenthes is as an ornamental, the stems of several species are used as rough cordage. They are, for instance, used in the construction of longhouses in Borneo. On Bangka (Indonesia) N. ampullaria is a substitute for rattans and dried or peeled stems serve for tying, for instance in pepper gardens, fence-making and house construction, and for carrying heavy loads. In Riau and the Lingga Archipelago (Indonesia) it is also often used for tying. In Peninsular Malaysia the stems of N. ampullaria and N. rafflesiana are reportedly used for tying fences, though the use of the latter species for this purpose is questionable. On Belitung (Indonesia) baskets are made of the stems of N. ampullaria and N. rafflesiana . Larger pitchers are used to cook rice in, e.g. those of N. ampullaria in West Sumatra.

In Peninsular Malaysia the roots of N. ampullaria are boiled and made into a poultice to treat stomach-ache and dysentery, whereas stem decoctions or infusions are drunk for remittent fever. The fluid in unopened Nepenthes pitchers is potable and has been used for eye inflammation, indigestion and other stomach problems.

N. ampullaria and N. rafflesiana are used locally as fibre plants and no production statistics are available.

The main value of Nepenthes in international trade is as ornamentals, In the international horticultural trade on average about 1.2 million Nepenthes plants were traded annually in the period 1983-1987. The trade value has been estimated at more than US$ 15 million per year. Both N. ampullaria and N. rafflesiana are internationally traded as ornamentals.

Nepenthes stems are resistant to moisture. Those of N. ampullaria are considered to be of very good quality because they are strong, supple and durable. Peeled N. ampullaria stems are said to be stronger and more durable than rattan.

Dioecious, woody or subwoody climbers or subshrubs, terrestrial or epiphytic. Young plants rosette-shaped, older plants always elongated, in climbing species often with elongated climbing stems, short non-climbing stems and with secondary, dense rosettes at the base of older stems. Stems terete, 2-4-angled or more or less winged as an effect of decurrent leaves. Leaves alternate, without stipules, petiolate or sessile, simple, papery or leathery, composed of a phyllodium-like blade, a tendril, a pitcher and a lid; blades of the rosettes always smaller than those of elongated and short stems, sometimes even absent; midrib extending into an unbranched tendril with an apex expanding into a variously coloured receptacle ("pitcher") containing digestive fluid; lower pitchers produced from rosettes or short stems, usually ovoid or globular, the mouth facing towards the stem, with 2 ventral fringed wings running from the base to the pitcher rim and with the tendril straight, not coiled; upper pitchers (not always present) usually more elongated and funnel-shaped, the mouth facing away from the stem, the wings absent or reduced to ridges and not fimbriate, and the tendril coiled; pitcher mouth apical or subapical, rimmed with a ribbed, often glossy red peristome, the inner edge often toothed and bearing nectar glands; lid usually held over the mouth when young, opening later, lower surface usually with a laterally flattened basal appendage; spur inserted on dorsal surface at junction with lid. Inflorescence a terminal, peduncled raceme or panicle; if a raceme then the pedicels 1-flowered or furcate and 2-flowered; if a panicle, then its lower branches corymbosely branched and 3-10-flowered, the upper ones fewer-flowered; male and female inflorescences quite similar, male ones usually larger and more floriferous; perianth imbricate, a single whorl of 4 free or basally united, patent, nectariferous, green, brown or red tepals; male flowers with 4-12 stamens, filaments united into a column (androphore), gynoecium lacking; female flowers without androecium, ovary superior, 4-locular with numerous ovules, stigmas 4, sessile. Fruit a fusiform, loculicidally dehiscent capsule with 4 valves. Seed filiform, 3-25 mm long, with long basal and apical appendages.

• N. ampullaria . A terrestrial climber up to 15 m tall, with many terrestrial and few aerial rosettes, with densely velvety indumentum of red-brown hairs in young parts. Stem cylindrical, 1-1.5 cm in diameter, internodes 1.5-8 cm long, at the foot of older plants lateral rosettes with pitchers are present. Leaves sessile; blade thickly leathery, lanceolate to spatulate, undersurface with red hairs; rosette leaves 2-5 cm × 0.5 cm, climbing leaves 12-25 cm × 3-6 cm; base attenuate, clasping the stem by half its circumference; lower pitchers obliquely urceolate, semi-circular on dorsal side, almost flat ventrally, 2-10 cm × 9 cm, usually green, deeply flecked with maroon, rarely entirely red, sometimes whitish-yellow with pale pink flecks, with 2 fringed wings up to 1.5 cm broad, fringe elements 0.5-1 cm long and 1-1.5 mm apart; mouth oval, almost horizontal; peristome flattened, 3-15 mm wide and sloping steeply inwards, ribs 0.2-0.3 mm apart; lid narrowly oblanceolate, up to 4 cm × 1.5 cm, lower surface without appendages, nectar glands sparse or absent; spur simple or branched, up to 1 cm long; upper pitchers generally not developed, rudimentary, broadly funnel-shaped, about 2 cm × 2 cm. Male inflorescence a panicle up to 40 cm × 4-5 cm; partial inflorescences usually 8-12 cm long and with 3-6 flowers; pedicel 7-8 mm long; tepals broadly elliptical, 4-5 mm × 3-5 mm, green to yellow; androphore 3-5 mm long. Female inflorescence and flowers about similar. Fruit 2-3 cm long, valves 2-3.5 mm wide in the middle. Seed 10-15 mm long.

• N. rafflesiana . A terrestrial climber 2-6(-15) m tall with white or grey arachnoid indumentum. Stem terete, those of short stems and rosettes 7-9 mm in diameter with internodes 0.5-1.5 cm long, when climbing 5-12 mm in diameter with internodes 4-17 cm long. Leaves papery, distinctly petiolate; petiole canaliculate, 4-17 cm long, in short stems sheathing; blade in short stems narrowly oblong, 12-45 cm × 3-11 cm, in climbing stems usually smaller, in both the lower surface with stellate hairs; lower pitchers ovoid to subglobose, 5-25 cm × 3-10 cm, white, mottled with purple-red, and with red sessile glands, with 2 fringed wings 1-3 cm wide, fringe elements 5-15 mm long and 1-4 mm apart; mouth strongly concave, rising gradually at the rear and tapering to a distinct column 3-5 cm high and 1-2 cm deep, inner surface bearing protruding teeth 3-5 mm long; peristome subcylindrical, 4-10 mm wide at the sides, ribs 0.7-1.5 mm apart, inner edge with conspicuous teeth 2-5 mm long; lid orbicular, ovate or elliptical, 4-9.5 cm × 3-7.5 cm, lower surface without appendages but with conspicuous glands; spur 8-30 mm × 1-2 mm, bifurcate at apex; upper pitchers funnel-shaped, 9-40 cm × 3-8 cm, pale green, without fringed wings but with 2 ridges, mouth at the rear with a short column 1-3 cm high; peristome cylindrical, 2-8 mm wide, striped yellow, green and red, ribs 0.5-1 mm apart, inner edge with 1-2 mm long teeth; lid ovate, elliptical or obovate, 3.5-9 cm × 3-7 cm, lower surface without appendages but with a dense band of nectar glands around the periphery; spur 8-26 mm long, entire. Male inflorescence 12-50 cm × 2-6 cm; pedicel 1-2 cm long, 1(-2)-flowered; tepals elliptical, 5-7 mm × 5 mm; androphore 4.5-6 mm long. Female inflorescence similar to male one but only a bit shorter. Fruit stipe 3-8 mm long, valves 16-50 mm × 5-10 mm. Seed 12-18 mm × 0.2-0.4 mm.

Nepenthes seeds normally germinate 4-6 weeks after sowing. Initially the plants of most species have a short erect stem and short internodes ("rosette stems"), after which they become shrubby by producing stems up to 2 m long with longer internodes ("short stems"). These can become lianas with even longer internodes and with coiling tendrils supporting the stems ("climbing stems"). In some species, including N. ampullaria , the shrubby stage is negligibly short. Aerial branching of the stems is rare in Nepenthes but does occur in N. ampullaria .

The pitcher of Nepenthes functions as a trap for a wide range of invertebrates and sometimes vertebrates. N. rajah Hook.f., the species with the largest pitchers, even traps rats. The wall of the pitcher is thin but very strong. The upper third of the inner pitcher wall is called the "waxy zone" and is covered with a dense coating of minute, easily detachable wax scales, which become attached to the suction pads or tarsi of prey, temporarily destroying their ability to grip any surface. The zone below the waxy zone is the "glandular zone". Prey is probably attracted by both the colour of the pitcher and the presence of nectar secreted by glands on the lower side of the pitcher lid, the inner edge of the peristome and the outer surface of the pitcher. The prey that falls into the fluid at the base of the pitcher is broken down by a combination of proteolytic enzymes secreted by the glands in the lower part of the pitcher and bacteria living in the pitcher fluid, and the products are absorbed by the same glands. Pitchers may also contain organisms which are able to live there without being killed and which may improve the trap function by breaking down trapped prey. Though ants are the main prey organisms, only a small fraction of the visiting ants are captured. Prey in the pitchers is an important source of nutrients for Nepenthes : studies of N. rafflesiana in its natural environment showed that plants deprived of prey for 18 weeks suffered from nutrient-stress and contained 78% less phosphorus and 67% less nitrogen in their leaves than control plants. The pitchers of N. ampullaria and some other Nepenthes may primarily function as devices for trapping water and litter.

Nepenthes is probably insect-pollinated, mostly during the day by generalist Diptera and Hymenoptera . The main visitors of N. rafflesiana flowers are day-flying chrysomelid beetles. Because Nepenthes is dioecious, it is outbreeding. Seed dispersion is probably by wind. In Singapore N. ampullaria and N. rafflesiana flower throughout the year, but fruiting is most abundant in April-June.

Nepenthes is usually considered the only genus in the Nepenthaceae , though some regard N. pervillei Blume from the Seychelles as forming a separate genus Anurosperma (Hook.f.) Hallier. Classification within the genus is very difficult, especially because of the heteromorphy of stems, leaf blades and pitchers. Within the genus 6 groups have been distinguished, but this division is not considered entirely satisfactory. The knowledge of most species is too limited to reliably distinguish infra-specific taxa.

All Nepenthes investigated to date have a chromosome number of 2 n = 80. It has been suggested that the basic number is low ( x = 5, perhaps 10) and that all species in the genus have a high ploidy level (16 x or 8 x ), though isozyme analysis has not supported this hypothesis. Interspecific hybridization is common in Nepenthes . N. × hookeriana Lindl. is a naturally occurring hybrid between N. ampullaria and N. rafflesiana , whereas N. × trichocarpa Miq. is probably a natural hybrid of N. ampullaria and N. gracilis Korth. Both hybrids occur in Sumatra, Peninsular Malaysia and Borneo, where they are widespread but scarce and only found near populations of the parent species.

The stems and roots of N. alata Blanco are chewed against toothache in the Philippines. The pitchers of N. boschiana Korth. have been used in Borneo for cooking in and as toys for children, whereas the water in unopened pitchers was considered a cure for eye-inflammation, but this species is only known by its type specimen. The boiled roots of N. gracilis are taken against dysentery and stomach-ache in Peninsular Malaysia, whereas in the Lingga Archipelago (Indonesia) extracts are taken in case of a sore mouth and a swollen tongue. In Java water from the pitchers of N. gynamphora Nees is drunk against cough. N. distillatoria R. Grah. is used for rough cordage in Sri Lanka.

Nepenthes is found in humid climates, mostly in exposed habitats on nutrient-poor soils. It is commonly found along river banks, ridge tops and in wet mossy forest. Usually it grows in locations with a sparse or thin canopy and it is not common in dense forest, though a few species, including N. ampullaria , can survive in quite dense shade. It is common on white podsolic soils, wet peaty soils or heavily leached volcanic soils, but is almost completely absent from rich alluvial or clay soils. In Malesia Nepenthes is mostly found up to 700 m altitude, in disturbed secondary forest, swamp or heath ("kerangas") forest, but in these habitats only a few species occur, including N. ampullaria and N. rafflesiana . More species but fewer individuals occur in montane habitats, at 1500-2500 m altitude, often in open mossy, stunted, ridge-top forest. A few species are found in montane or subalpine grassland, up to 3500 m altitude.

N. ampullaria grows in damp, shady forest, swamp and heath forests (Borneo), Araucaria forest (New Guinea), secondary forest, open microphyllous vegetation and swamp grassland, usually up to 200 m altitude, occasionally as high as 2100 m. N. rafflesiana occurs in swamp and heath forests, often with N. ampullaria , but also in secondary forest and old clearings, often on sand, at altitudes up to 300 m, sometimes up to 1500 m. It is often abundant in weedy regrowth along roadsides.

Nepenthes can be propagated by layering, cuttings or seed. In the Botanic Garden in Bogor (Indonesia) N. ampullaria and N. rafflesiana cuttings have successfully been grown in water and moss media.

Nepenthes is not cultivated as a fibre plant and stems for tying are collected only from the wild. It is, however, widely collected and grown as an ornamental. Ample moisture and high humidity are required for growing Nepenthes ; good drainage is essential. Though Nepenthes plants absorb nutrients from prey in the pitchers, fertilization may be beneficial. Old plants benefit from heavy pruning.

On Bangka the stems of N. ampullaria are cut near the ground. They are then pulled down and the top is removed.

On Bangka (Indonesia) the harvested stems of N. ampullaria are cleaned by pulling them between two tree-trunks, cut, bundled and dried in full sun for 3-4 days, resulting in a change in colour from white to wine-red. Alternatively, the stems may be peeled and the central part used.

N. ampullaria and N. rafflesiana are not considered threatened, but several other Nepenthes spp. are endangered, especially those with a very limited distribution. The main threats are habitat destruction (especially for lowland species) and indiscriminate collection for horticultural trade (especially for montane species). N. rajah Hook.f. and N. khasiana Hook.f. are listed in CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) Appendix I, which means that trade of wild material is prohibited and that of artificially propagated material is only allowed under licence. The rest of the genus is listed in Appendix II, which means international trade in wild and artificially propagated material is permitted subject to licence. In the Botanic Garden in Bogor (Indonesia) living collections of N. ampullaria and N. rafflesiana are kept in greenhouses.

The role of Nepenthes as a fibre plant will remain limited to local use. The real prospect lies in its use as ornamental plant. However, due to the very limited distribution of most Nepenthes species, care must be taken that collection does not lead to extinction.

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I.P. Astuti, Y. Umi Kalsom & R.M. Taha