Nepenthes bicalcarata (; from Latin for "two-spurred"), also known as the fanged pitcher-plant,Phillipps, A. & A. Lamb 1996. Pitcher-Plants of Borneo. Natural History Publications (Borneo), Kota Kinabalu. is a tropical pitcher plant which is endemic to Borneo. It is a vine up to length. It is a myrmecophyte noted for its mutualistic association with a species of ant, Camponotus schmitzi. As an ant-fed plant it lacks many of the features that characterise the carnivorous syndrome in Nepenthes, including viscoelastic and highly acidic pitcher fluid, the waxy zone of the pitcher interior, and possibly even functional digestive enzymes.
Botanical history
Nepenthes bicalcarata was formally described by Joseph Dalton Hooker in his 1873 monograph, "Nepenthaceae", based on specimens collected by Hugh Low and Odoardo Beccari near the Lawas River in Borneo. The type specimen, Low s.n., is deposited at the Royal Botanic Gardens, Kew.Schlauer, J. Nepenthes bicalcarata . Carnivorous Plant Database. Seven years later, Spencer Le Marchant Moore described Nepenthes dyak, based on a specimen (Teijsmann 10962) collected by Johannes Elias Teijsmann from Kapuas River near Sintang in western Borneo.Jebb, M.H.P. & M.R. Cheek 1997. A skeletal revision of Nepenthes (Nepenthaceae). Blumea 42 (1): 1–106. This specimen is also held at the Royal Botanic Gardens, Kew and a duplicate is deposited at the National Herbarium of the Netherlands in Leiden.Specimen detail: Teijsmann 10962. Nationaal Herbarium Nederland. Nepenthes dyak was later mentioned several more times in the botanical literature,Burbidge, F.W. 1882. Notes on the new Nepenthes. The Gardeners' Chronicle, new series, 17(420): 56.Beccari, O. 1896. Malesia, III (1886–1890): Rivista delle specie del genere Nepenthes, p. 1–15. but is now considered conspecific with N. bicalcarta.
Nepenthes bicalcarata was introduced to Europe in 1879 by British explorer Frederick William Burbidge, who collected plants for the famous Veitch Nursery. These were cultivated to larger size and distributed in 1881.
During this time, interest in Nepenthes had reached its peak. A note in The Gardeners' Chronicle of 1881 mentions the Veitch Nursery's N. bicalcarata as follows:[Anonymous] 1881. Messr's Veitch's Nepenthes House. The Gardeners' Chronicle n. ser. 16: 598.
"Then there is N. bicalcarata, a most robust habited kind with sturdy foliage and bag-like pitchers provided with a vicious-looking rat-trap-like apparatus in its lid which renders it very distinct from its neighbours."
Several years after its introduction, N. bicalcarata was still very much a horticultural rarity. In Veitch's catalogue for 1889, N. bicalcarata was priced at £3.3s per plant, while the famous giant-pitchered N. northiana and N. rajah were selling for £2.2s.
Description Nepenthes bicalcarata plants are the largest in the genus, climbing up to 20 m into the forest canopy. The cylindrical stem is thicker than that of any other Nepenthes species, measuring up to 3.5 cm in diameter. Internodes are up to 40 cm long.Clarke, C.M. 1997. Nepenthes of Borneo. Natural History Publications (Borneo), Kota Kinabalu.Steiner, H. 2002. Borneo: Its Mountains and Lowlands with their Pitcher Plants. Toihaan Publishing Company, Kota Kinabalu.
The leaves of N. bicalcarata are petiolate and coriaceous in texture. The lamina is obovate-lanceolate in form and also reaches huge dimensions, growing to 80 cm in length and 12 cm in width.Danser, B.H. 1928. 4. Nepenthes bicalcarata. In: The Nepenthaceae of the Netherlands Indies. Bulletin du Jardin Botanique de Buitenzorg, Série III, 9(3–4): 249–438. It is slightly decurrent on the stem, forming two narrow wings. The lamina has indistinct longitudinal veins and numerous pennate veins. The tendrils may be up to 60 cm long and 8 mm wide. They are hollow and swollen near the pitcher, and are the primary residence of the ants. The ants get much of their food from numerous, large extrafloral nectaries.
Although most parts of the plant are very large, the pitchers themselves do not rival those of species such as N. rajah. Nevertheless, they may have a volume of over one litre and grow up to 25 cm high and 16 cm wide. A pair of prominent fringed wings (≤15 mm wide) runs down the front of lower pitchers. These are usually reduced to ribs in aerial pitchers. The peristome (≤20 mm wide) is characteristically flattened and curved inwards. The inner portion of the peristome accounts for around 70% of its total cross-sectional surface length.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. It bears small but distinct teeth. The two sharp spines for which the species is famous are present on the underside of the pitcher lid, and may be 3 cm long. They are derived from the uppermost 10–12 peristome ribs.Cheek, M.R. & M.H.P. Jebb 2001. Nepenthaceae. Flora Malesiana 15: 1–157. The pitcher lid or operculum is reniform to cordate and has no appendages. An unbranched spur (≤15 mm long) is inserted at the base of the lid.
Nepenthes bicalcarata has a paniculate inflorescence. The peduncle may be up to 40 cm long and the rachis can reach 100 cm in length. Female inflorescences are usually shorter.Macfarlane, J.M. 1908. Nepenthaceae. In: A. Engler Das Pflanzenreich IV, III, Heft 36: 1–91. Branches on the flower stem are up to 40 mm long and bear up to 15 flowers. Sepals are either obovate or lanceolate and up to 4 mm long. A study of 120 pollen samples taken from a herbarium specimen (Fosberg 43860, altitude not recorded) found the mean pollen diameter to be 28.9 μm (SE = 0.4; CV = 7.5%).Adam, J.H. & C.C. Wilcock 1999. Palynological study of Bornean Nepenthes (Nepenthaceae). Pertanika Journal of Tropical Agricultural Science 22(1): 1–7.
Mature plants are virtually glabrous. Caducous hairs are present on the youngest parts of the plant and on the inflorescences.
Nepenthes bicalcarata varies little across its range. Consequently, no infraspecific taxa have been described.
Ecology and conservation status
Nepenthes bicalcarata is endemic to Borneo. It is most common in the peat swamp forests of the western coast of the island, which stretch across Sarawak, Sabah, Kalimantan, and Brunei. There it often grows in the shade of the ubiquitous dipterocarp Shorea albida. Nepenthes bicalcarata also occurs in kerangas forest and has even been recorded from white sand heath forests in Sarawak and East Kalimantan. The species is often sympatric with N. ampullaria in these habitats.
Specimens growing in undisturbed peat swamp forest, where sunlight is greatly diffused and high humidity prevails, reach the largest dimensions. Nepenthes bicalcarata has a shallow root system that only penetrates the top layer of peat and leaf litter, to a depth of about 25 cm. Below this, high concentrations of tannins and alkaloids render the substrate toxic.
Nepenthes bicalcarata is generally found below 300 m in altitude, although Johannes Gottfried Hallier reported a single collection in 1894 from between 700 and 950 m above sea level.Hallier, H. 1895. Ein neues Cypripedium aus Borneo. Natuurkundig Tijdschrift voor Nederlandsch Indië LIV: 450–452.
The conservation status of N. bicalcarata is listed as Vulnerable on the 2006 IUCN Red List of Threatened Species based on an assessment carried out in 2000. In 1997, Charles Clarke informally classified the species as Near Threatened based on the IUCN criteria. This agrees with the conservation status assigned to N. bicalcarata by the World Conservation Monitoring Centre.Simpson, R.B. 1995. Nepenthes and conservation. Curtis's Botanical Magazine 12: 111–118.
Carnivory
The two thorns that give N. bicalcarata its name are unique to this species and bear some of the largest nectaries in the plant kingdom.Merbach, M.A., G. Zizka, B. Fiala, D. Merbach & U. Maschwitz 1999. Giant nectaries in the peristome thorns of the pitcher plant Nepenthes bicalcarata Hooker f. (Nepenthaceae): anatomy and functional aspects. Ecotropica 5: 45–50. Clarke, C.M. 2001. A Guide to the Pitcher Plants of Sabah. Natural History Publications (Borneo), Kota Kinabalu.Clarke, C.M. & C.C. Lee 2004. Pitcher Plants of Sarawak. Natural History Publications (Borneo), Kota Kinabalu. The purpose of these structures has long been debated among botanists. Frederick William Burbidge suggested that they might serve to deter arboreal mammals such as tarsiers, lorises and monkeys from stealing the contents of the pitchers.Slack, A. 1979. Nepenthes bicalcarata. In: Carnivorous Plants. Ebury Press, London. p. 82. In an article published in 1982, Cliff Dodd speculated on the function of the thorns, but did not believe they play a role in prey capture.Dodd, C. 1982. The most dangerous (looking) Nepenthes. Carnivorous Plant Newsletter 11(3): 64–65, 73, 78. Charles Clarke observed that monkeys and tarsiers rip the pitchers open at the sides in order to feed from them, rather than reaching in through the pitcher mouth.Clarke, C.[M.] 1993. The possible functions of the thorns of Nepenthes bicalcarata (Hook.f.) pitchers. Carnivorous Plant Newsletter 22(1–2): 27–28. However, he found that the mammals attacked the pitchers of N. bicalcarata less frequently than those of other species, such as N. rafflesiana. Clarke's observations suggest that the spines likely serve to lure insects into a precarious position over the pitcher mouth, where they may lose their footing and fall into the pitcher fluid, eventually drowning. A similar trapping method is employed by the Sumatran endemic N. lingulata, which has a single filiform appendage positioned over the pitcher mouth. However, in that species the appendage is a structure of the lid and not the peristome.Lee, C.C., Hernawati & P. Akhriadi 2006. Two new species of Nepenthes (Nepenthaceae) from North Sumatra. Blumea 51(3): 561–568.
Together with N. ampullaria and N. ventricosa, N. bicalcarata is unusual in that the glandular region of the pitcher extends almost to the peristome, such that there is little or no conductive waxy zone.Bohn, H.F. & W. Federle 2004. Insect aquaplaning: Nepenthes pitcher plants capture prey with the peristome, a fully wettable water-lubricated anisotropic surface. Proceedings of the National Academy of Sciences 101(39): 14138–14143.Moran, J.A., B.J. Hawkins, B.E. Gowen & S.L. Robbins 2010. Ion fluxes across the pitcher walls of three Bornean Nepenthes pitcher plant species: flux rates and gland distribution patterns reflect nitrogen sequestration strategies. Journal of Experimental Botany 61(5): 1365–1374. Di Giusto, B., M. Guéroult, N. Rowe & L. Gaume 2009. Chapter 7: The Waxy Surface in Nepenthes Pitcher Plants: Variability, Adaptive Significance and Developmental Evolution. In: S.N. Gorb (ed.) Functional Surfaces in Biology: Adhesion Related Phenomena. Volume 2. Springer. pp. 183–204. The waxy zone functions by causing prey to slip and fall into the digestive fluid. A 2004 study found that the peristome of N. bicalcarata plays a very important role in prey capture. When it is dry, the peristome is highly ineffective in catching insect prey, but when wetted, the capture rate increases more than three-fold.