Appearance''Nepenthes fusca'' is a climbing plant. The stem may attain a length of 10 m and is up to 8 mm in diameter. Internodes are circular in cross section and up to 7 cm long.
The leaves of this species are petiolate and coriaceous in texture. The lamina or leaf blade is obovate-oblong in shape and measures up to 15 cm in length by 6 cm in width. Its apex is acute to obtuse and may even be slightly peltate. The base of the lamina is gradually attenuate towards the petiole. The petiole is grooved lengthwise and bears a pair of narrow wings that form a semi-amplexicaul sheath around the stem. Up to 3 longitudinal veins are present on either side of the midrib, although they are indistinct. Pinnate veins are numerous. Tendrils measure up to 5 cm in length.
Rosette and lower pitchers are cylindrical throughout. They usually grow to 20 cm in height by 4 cm in width, although exceptional specimens up to 28 cm have been recorded. A pair of fringed wings runs down the ventral surface of the pitcher and bears fringe elements measuring up to 10 mm and spaced 6 mm apart. The glandular region is restricted to the lower portion of the pitcher's inner surface. The glands are small, overarched, and occur at a density of 600 to 650 per square centimetre. The waxy zone is reduced. The pitcher mouth is positioned horizontally at the front, becoming elongated into a neck at the rear. The peristome is flattened and expanded , but bears only indistinct teeth . The inner portion of the peristome accounts for around 51% of its total cross-sectional surface length. The pitcher lid or operculum is very narrowly ovate in shape and has a distinctive basal crest on its lower surface. An unbranched spur measuring up to 10 mm in length is inserted near the base of the lid.
Lower pitchers of ''N. fusca'' from the Crocker Range and the area around Mount Kinabalu . From left to right: CR, MK, MK, CR, and CR.
Upper pitchers differ markedly in shape, being narrowly infundibular in the lower two-thirds and becoming widely infundibular above. They are similar in size to their lower counterparts, typically measuring up to 18 cm, with some larger forms reaching 26 cm. The tiny digestive glands are overarched and number 1500 to 2000 per square centimetre. The pitcher lid is very narrowly triangular with the margins and apex curved downwards. In aerial pitchers, the wings are reduced to ribs.
Upper pitchers of ''N. fusca'' from the Crocker Range and the area around Mount Kinabalu . From left to right: MK, MK, CR, MK, and CR.
''Nepenthes fusca'' produces a compact racemose inflorescence. The peduncle is up to 6 cm long, while the rachis is not known to exceed 10 cm. Partial peduncles are one- or two-flowered, up to 8 mm long, and lack a bract. Sepals are elliptic and up to 4 mm long. A study of 120 pollen samples taken from the type specimen found the mean pollen diameter to be 34.8 μm .
Developing parts of the plant bear an indumentum of long, brown hairs. However, most of these disappear during the normal course of development, and mature parts only have a sparse covering of short, brown hairs.
NamingTwo subspecies of ''N. fusca'' have been described, neither of which is presently thought to represent the species:
⤷ ''Nepenthes fusca'' subsp. ''apoensis'' J.H.Adam & Wilcock ''ex'' Jebb & Cheek ''nom.nud.'' [=''N. stenophylla'']
⤷ ''Nepenthes fusca'' subsp. ''kostermansiana'' J.H.Adam & Wilcock ''ex'' Jebb & Cheek ''nom.nud.'' [=''N. epiphytica'']
Both were originally coined by J. H. Adam and C. C. Wilcock and subsequently published in Jebb and Cheek's 1997 monograph, "A skeletal revision of ''Nepenthes'' ". As these names were published without an adequate description, they are both considered ''nomina nuda''. The former is likely based on ''Chai 35939'', a specimen collected from Mount Apo. Schlauer considers it synonymous with ''N. fallax'', a taxon that is in turn considered conspecific with ''N. stenophylla'' by most authors.
''Nepenthes fusca'' subsp. ''kostermansiana'' was named from the herbarium material ''Kostermans 21495'', which was collected by André Joseph Guillaume Henri Kostermans on October 25, 1963, at 1000 m altitude along the Kelai River on Mount Nyapa , Berau Regency, East Kalimantan. It is deposited at the National Herbarium of the Netherlands in Leiden. This taxon was initially thought to fall within the variability of ''N. fusca'', but in 2011 it was described as a distinct species, ''N. epiphytica'', with ''Kostermans 21495'' designated as its holotype.Among the closest relatives of ''N. fusca'' are the Bornean species ''N. epiphytica'', ''N. hurrelliana'', ''N. platychila'', ''N. stenophylla'', and ''N. vogelii''. More broadly, it belongs to the loosely defined "''N. maxima'' complex", which also includes ''N. boschiana'', ''N. chaniana'', ''N. eymae'', ''N. faizaliana'', ''N. klossii'', and ''N. maxima''. The enigmatic ''N. mollis'', which some authors have suggested is conspecific with ''N. hurrelliana'', may also be closely allied.
The lower pitchers of ''N. hurrelliana'' are distinctive, but the upper ones bear a close resemblance to those of ''N. fusca''. Of the Bornean pitcher plant flora, only these two species have such a narrowly triangular lid. The upper pitchers of ''N. hurrelliana'' differ in having a horizontal mouth that rises abruptly into a long neck at the back and in having a hirsute basal crest on the underside of the lid.
''Nepenthes hurrelliana'' is particularly similar to a form of ''N. fusca'' from the southern portion of the Crocker Range in Sabah. This form exhibits a wider peristome, longer neck, and a more triangular lid than most other examples of the species. However, the peristome is still not as well developed as in ''N. hurrelliana'' and the plant lacks the dense indumentum of the latter. Furthermore, ''N. hurrelliana'' differs in the distribution of nectar glands on the lower surface of its lid.
The first known collection of ''N. vogelii'', made in 1961, was labelled as ''N. fusca''. In 1969, botanist Shigeo Kurata examined this specimen and noted that it did not fall within the known variation exhibited by ''N. fusca''. Nevertheless, the species remained undescribed until 2002. ''Nepenthes vogelii'' differs in having much smaller pitchers and lacking appendages on the underside of the lid. In addition, the lid of ''N. vogelii'' is broadly triangular as opposed to the narrowly triangular lid of ''N. fusca''. The colour of the pitchers—light cream with dark speckles—is also distinctive.
''Nepenthes faizaliana'' also bears a resemblance to ''N. fusca''. In their description of the former, J. H. Adam and C. C. Wilcock distinguished these taxa on the basis of inflorescence structure, the size of the glandular region on the inner surface of upper pitchers, and the development and characteristics of the indumentum. ''Nepenthes fusca'' also differs in having a very narrow pitcher lid, as opposed to the orbicular lid of ''N. faizaliana''.
''Nepenthes platychila'', another closely allied species, differs from ''N. fusca'' in having a much wider peristome and lid, and lacking appendages on its lower lid surface. ''Nepenthes fusca'' is also thought to be closely related to Sulawesi's ''N. eymae'', and ''N. maxima'', which is widespread in Sulawesi, New Guinea, and the Maluku Islands.
Status''Nepenthes fusca'' is classified as Vulnerable on the 2006 IUCN Red List of Threatened Species, based on an assessment carried out in 2000. This agrees with an informal assessment made in 1997 by Charles Clarke, who also classified the species as Vulnerable based on the IUCN criteria. However, Clarke noted that since substantial populations of ''N. fusca'' lie within the boundaries of national parks, they "are unlikely to become threatened in the foreseeable future". Taking this into account, he suggested a revised assessment of Conservation Dependent. The IUCN status is at odds with an assessment by the World Conservation Monitoring Centre, which classified ''N. fusca'' as "not threatened", its lowest conservation status.
Habitat destruction is considered to be the greatest threat to the species's survival in the wild. Plant poaching is of far lesser concern, as this species is not particularly sought after in the carnivorous plant hobby and its epiphytic habit makes it largely inaccessible to collectors.
Habitat''Nepenthes fusca'' is endemic to Borneo, where its range stretches from Central Kalimantan to northwestern Sabah. It has been recorded from Brunei, Indonesia , and Malaysia . The species has a wide altitudinal distribution and is typically found at elevations of 1200 to 2500 m above sea level. However, ''N. fusca'' has occasionally been reported from lowland hills down to 600 m and in Sarawak it has been found at only 300 m in hill forest.
''Nepenthes fusca'' is most commonly found as an epiphyte in shady mossy forest on ridge tops, where it may grow 10 to 15 m off the ground. This makes it particularly difficult to find and often the only evidence of its presence are dead pitchers that have fallen to the forest floor....hieroglyph snipped... In this respect, it can be considered the "ecological equivalent" of ''N. bongso'' from Sumatra. More rarely, ''N. fusca'' grows terrestrially in exposed sites near montane forest or along logging roads. It is often sympatric with species such as ''N. reinwardtiana'', ''N. stenophylla'', and ''N. tentaculata'', and natural hybrids with all of these have been recorded.
EvolutionThe first known collection of ''N. fusca'' was made by Frederik Endert on October 12, 1925, from Mount Kemul in East Kalimantan, at an elevation of 1500 m. It was discovered during an expedition to central Borneo by the Forest Research Institute of Bogor , on which Endert also made the only known collection of ''N. mollis''. The ''N. fusca'' specimen, designated as ''Endert 3955'', includes male floral material and is deposited at Herbarium Bogoriense , the herbarium of the Bogor Botanical Gardens. Endert wrote about this pitcher plant in a detailed 1927 account of the expedition, although he misidentified it as ''N. veitchii''.
''Nepenthes fusca'' was formally described in 1928 by Dutch botanist B. H. Danser in his seminal monograph "The Nepenthaceae of the Netherlands Indies". Danser based his description solely on ''Endert 3955'', citing no other specimens. He wrote of ''N. fusca'':
This new species is, together with ''N. Veitchii'' and ''N. stenophylla'', very nearly related to ''N. maxima'', but can not be confounded with any of these species. According to Endert it grew in the forest on a narrow, stony mountain ridge covered with humus, and was not rare.
Botanist Jan Schlauer has noted differences between the type specimen of ''N. fusca'' and Sabah plants referred to this species, even interpreting plants illustrated in Kurata's ''Nepenthes of Mount Kinabalu'' as representing ''N. stenophylla'' . Matthew Jebb does not consider these differences significant enough to merit distinction at the species level. He suggests that the type specimen consists of intermediate lower and upper pitchers as opposed to true forms of either, making them appear atypical.
Much of this taxonomic uncertainty stems from the fact that ''N. fusca'' has not been recollected from the type locality and many similar plants have been lumped under this taxon. Matthew Jebb and Martin Cheek attempted to resolve this confusion in their 1997 monograph by interpreting ''N. fusca'' as a widespread and variable species.
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