Nepenthes rhombicaulis
Encyclopedia
Nepenthes rhombicaulis (icon) is a tropical pitcher plant
endemic to Sumatra
. The specific epithet rhombicaulis is formed from the Latin
words rhombicus, meaning "rhomboid", and caulis, "stem". It refers to the cross-sectional shape of the stem internodes
.
Nepenthes rhombicaulis was first collected by Shigeo Kurata
on March 29, 1972, on Mount Pangulubao
at an altitude of between 1700 and 1900 m above sea level. The species was mentioned by name in a 1972 issue (volume 26, number 10, page 44) of The Heredity. It was formally described
by Kurata the following year in the The Gardens' Bulletin Singapore. One of the original specimens, Kurata 4300, was designated as the holotype
of the species and is deposited at the herbarium of the Nippon Dental College (NDC). An isotype
is held at the National Herbarium of Singapore
(SING).
Kurata's illustration of the type specimen shows a small apical appendage on the underside of the pitcher lid. However, Matthew Jebb
and Martin Cheek
pointed out that this feature is not present in the isotype held in Singapore
. Kurata suggested that the appendage might be a developmental defect and of little significance. Observations made at the type locality by Charles Clarke
and Ch'ien Lee
seem to confirm this; while some wild plants exhibit this appendage, most do not.
In the 1983 book Carnivorous Plants of the World in Colour by Katsuhiko and Masahiro Kondo, a photograph of N. gymnamphora
is identified as N. rhombicaulis.
In 1993, Bruce Salmon postulated that the lower pitchers of N. rhombicaulis are specially adapted to trapping subterranean insects. His observations were published in the Carnivorous Plant Newsletter
.
Rudolf Schmid-Höllinger reported observing upper pitchers of N. rhombicaulis on Mount Pangulubao in 1993. He published his findings the following year in the Carnivorous Plant Newsletter
. Charles Clarke
also reported finding one small upper pitcher in 1995. Prior to this, it was thought that the upper stem of N. rhombicaulis was only used for climbing and did not produce pitchers. However, doubts have been raised about the identity of the upper pitchers observed by Schmid-Höllinger.
are up to 20 cm long and 1 cm in diameter. They are usually rhomboid in cross section. The stem bears numerous sunken glands. The species has an extended rhizome
which produces stems at irregular intervals.
Leaves are sessile. The lamina is lanceolate-spathulate, up to 25 cm long, and up to 4 cm wide. It has an acute to sub-peltate apex and an amplexicaul base. Two to three longitudinal veins are present on either side of the midrib. Pinnate veins are oblique. Tendril
s may be up to 15 cm long.
Rosette and lower pitchers are ovoid to ventricose in the lower parts and cylindrical above. They reach 12 cm in height and 4 cm in width. A pair of fringed wings (≤3 mm long) runs down the front of the pitchers. The gland
ular region is restricted to the ovoid portion of the inner surface. Digestive glands occur at a density of 150 to 300 per square centimetre. The pitcher mouth is round and oblique. The peristome
is sub-cylindrical to irregularly expanded and up to 5 mm wide. Its inner margin is lined with distinct, papery teeth up to 3 mm long. The lid or operculum
is ovate and may bear a small apical appendage on its lower surface. Up to 100 nectar glands are present on the underside of the lid. A spur
(≤5 mm long), which may be unbranched, bifid, or trifid, is inserted near the base of the lid.
Upper pitchers have not been reliably recorded in the field and measurements for them have not been published. Based on Schmid-Höllinger's observations, they are ventricose in the lower parts and elongated above, becoming tubiform or slightly infundibuliform towards the mouth. The peristome is greatly reduced and bears smaller teeth. Wings may or may not be reduced to ribs. Several hundred nectar glands are present on the underside of the lid, although they are smaller than in lower pitchers.
Nepenthes rhombicaulis has a racemose
inflorescence
. The penducle
and rachis
both reach 20 cm in length, although the latter is usually shorter in female plants. Partial peduncles are two-flowered and lack bract
eoles. Sepal
s are elliptical and up to 4 mm long.
Most parts of the plant are virtually glabrous. The margins of the lamina are often lined with short red hairs. Inflorescences may have a sparse indumentum
of minute hairs.
The stem and lamina are green. Lower pitcher range in colour from dull green throughout to light red with purple blotches. The peristome may be light green to dark purple and is often darker around its outer margin. According to Schmid-Höllinger, upper pitchers are yellowish-green with pale red spots in the upper part and pitchers produced on offshoots
from the climbing stem have clear red speckles throughout.
Nepenthes rhombicaulis is known from a number of peaks in the Indonesia
n province of North Sumatra
, particularly around Lake Toba
. Plants that appear to match the description of N. rhombicaulis have also been recorded from Mount Bandahara in Aceh
. The species is known with certainty only from the Mount Pangulubao
complex and Mount Lubukraya, although Shigeo Kurata
suggested that it is likely to be more widespread in the Lake Toba region. Nepenthes rhombicaulis has an altitudinal distribution of 1600–2000 m above sea level.
Nepenthes rhombicaulis grows terrestrially in dense, shady montane forest. It is usually found in lower montane forest above steep slopes, but has also been recorded from upper montane forest. It is one of the few Nepenthes species that are common in the understory
.
Lower pitchers frequently develop embedded in detritus
and leaf litter on the forest floor, resulting in their often deformed appearance. Bruce Salmon noted that lower pitchers which develop in this way grow around twice as large as those which develop completely above ground. He postulated that the species is adapted to trapping subterranean insects, although he did not examine the contents of these pitchers to test the hypothesis.
In its natural habitat, N. rhombicaulis occurs sympatrically with N. flava
, N. ovata
, N. spectabilis
, and N. tobaica
. Natural hybrids with all of these species have been recorded. On Mount Pangulubao, N. gymnamphora
(N. xiphioides) and N. mikei
grow around 100 m above populations of N. rhombicaulis.
Due to its somewhat restricted distribution, N. rhombicaulis is listed as Vulnerable
on the 2006 IUCN Red List of Threatened Species
.
Nepenthes rhombicaulis is very similar to N. gymnamphora
in both morphology and growth habit. It is sympatric with this species on Mount Pangulubao
. Nepenthes rhombicaulis also bears a close resemblance to N. hirsuta
from Borneo
.
In 2001, Charles Clarke
performed a cladistic analysis of the Nepenthes species of Sumatra and Peninsular Malaysia
using 70 morphological characteristics of each taxon. The resultant cladogram
placed N. rhombicaulis in an unresolved polytomy
at the base of the Montanae/Nobiles
clade
, together with N. benstonei
.
Pitcher plant
Pitcher plants are carnivorous plants whose prey-trapping mechanism features a deep cavity filled with liquid known as a pitfall trap. It has been widely assumed that the various sorts of pitfall trap evolved from rolled leaves, with selection pressure favouring more deeply cupped leaves over...
endemic to Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
. The specific epithet rhombicaulis is formed from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
words rhombicus, meaning "rhomboid", and caulis, "stem". It refers to the cross-sectional shape of the stem internodes
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...
.
Botanical history
Shigeo Kurata
is a Japanese botanist and Nepenthes taxonomist whose work in the 1960s and 1970s contributed much to the current popularity of these plants. Of particular note is his 1976 guide, Nepenthes of Mount Kinabalu....
on March 29, 1972, on Mount Pangulubao
Mount Pangulubao
Mount Pangulubao or Pangulubau is a mountain near Lake Toba in Sumatra.Mount Pangulubao is notable for the relatively large number of tropical pitcher plant species that inhabit its forests. These include Nepenthes ampullaria, Nepenthes gymnamphora, Nepenthes mikei, Nepenthes ovata, Nepenthes...
at an altitude of between 1700 and 1900 m above sea level. The species was mentioned by name in a 1972 issue (volume 26, number 10, page 44) of The Heredity. It was formally described
Species description
A species description or type description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species which have been described previously, or are...
by Kurata the following year in the The Gardens' Bulletin Singapore. One of the original specimens, Kurata 4300, was designated as the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of the species and is deposited at the herbarium of the Nippon Dental College (NDC). An isotype
Isotype
Isotype can refer to:* In crystallography, an "isotype" is a synonym for isomorph* In biology, per the International Code of Botanical Nomenclature, the "isotype" is a duplicate of the holotype....
is held at the National Herbarium of Singapore
Singapore Botanic Gardens
The Singapore Botanic Gardens is a 74-hectare botanical garden in Singapore. It is half the size of the Royal Botanic Gardens in Kew or around one-fifth the size of Central Park in New York. It is the only botanic garden in the world that opens from 5 a.m...
(SING).
Kurata's illustration of the type specimen shows a small apical appendage on the underside of the pitcher lid. However, Matthew Jebb
Matthew Jebb
Dr. Matthew H. P. Jebb is an Irish taxonomist and botanist specialising in the ant plant genera Squamellaria, Myrmecodia, Hydnophytum, Myrmephytum and Anthorrhiza, as well as the carnivorous plant genus Nepenthes....
and Martin Cheek
Martin Cheek
Dr. Martin Roy Cheek is a taxonomist and botanist specialising in the carnivorous plant genus Nepenthes.-Research:Cheek has described several new Nepenthes species, mostly with Matthew Jebb, including: N. argentii, N. aristolochioides, N. danseri, N. diatas,...
pointed out that this feature is not present in the isotype held in Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
. Kurata suggested that the appendage might be a developmental defect and of little significance. Observations made at the type locality by Charles Clarke
Charles Clarke (botanist)
Dr. Charles M. Clarke is a botanist and taxonomist specialising in the carnivorous plant genus Nepenthes. Clarke has an honours degree in Botany from Monash University in Melbourne, and a Ph.D. in Ecosystem Management at the University of New England, in Armidale, New South Wales.Clarke first...
and Ch'ien Lee
Ch'ien Lee
Ch'ien C. Lee is a photographer and botanist specialising in the carnivorous plant genus Nepenthes. Lee has described several new Nepenthes species, including N. chaniana, N. gantungensis, N. glandulifera, N. jamban, N. lingulata, N. palawanensis, N. pitopangii,...
seem to confirm this; while some wild plants exhibit this appendage, most do not.
In the 1983 book Carnivorous Plants of the World in Colour by Katsuhiko and Masahiro Kondo, a photograph of N. gymnamphora
Nepenthes gymnamphora
Nepenthes gymnamphora is a tropical pitcher plant native to the Indonesian islands of Java and Sumatra. There is much debate surrounding the taxonomic status of this species and the taxa N. pectinata and N. xiphioides....
is identified as N. rhombicaulis.
In 1993, Bruce Salmon postulated that the lower pitchers of N. rhombicaulis are specially adapted to trapping subterranean insects. His observations were published in the Carnivorous Plant Newsletter
Carnivorous Plant Newsletter
The Carnivorous Plant Newsletter is the official publication of the International Carnivorous Plant Society , the largest such organization in the world.-History and editorship:...
.
Rudolf Schmid-Höllinger reported observing upper pitchers of N. rhombicaulis on Mount Pangulubao in 1993. He published his findings the following year in the Carnivorous Plant Newsletter
Carnivorous Plant Newsletter
The Carnivorous Plant Newsletter is the official publication of the International Carnivorous Plant Society , the largest such organization in the world.-History and editorship:...
. Charles Clarke
Charles Clarke (botanist)
Dr. Charles M. Clarke is a botanist and taxonomist specialising in the carnivorous plant genus Nepenthes. Clarke has an honours degree in Botany from Monash University in Melbourne, and a Ph.D. in Ecosystem Management at the University of New England, in Armidale, New South Wales.Clarke first...
also reported finding one small upper pitcher in 1995. Prior to this, it was thought that the upper stem of N. rhombicaulis was only used for climbing and did not produce pitchers. However, doubts have been raised about the identity of the upper pitchers observed by Schmid-Höllinger.
Description
Nepenthes rhombicaulis climbs well and its stem is known to reach 35 m in length, making it one of the longest in the genus. InternodesPlant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...
are up to 20 cm long and 1 cm in diameter. They are usually rhomboid in cross section. The stem bears numerous sunken glands. The species has an extended rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
which produces stems at irregular intervals.
Tendril
In botany, a tendril is a specialized stem, leaf or petiole with a threadlike shape that is used by climbing plants for support, attachment and cellular invasion by parasitic plants, generally by twining around suitable hosts. They do not have a lamina or blade, but they can photosynthesize...
s may be up to 15 cm long.
Rosette and lower pitchers are ovoid to ventricose in the lower parts and cylindrical above. They reach 12 cm in height and 4 cm in width. A pair of fringed wings (≤3 mm long) runs down the front of the pitchers. The gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...
ular region is restricted to the ovoid portion of the inner surface. Digestive glands occur at a density of 150 to 300 per square centimetre. The pitcher mouth is round and oblique. The peristome
Peristome
The word peristome is derived from the Greek peri, meaning 'around' or 'about', and stoma, 'mouth'. It is a term used to describe various anatomical features that surround an opening to an organ or structure. The term is used in plants and invertebrate animals, such as in describing the shells of...
is sub-cylindrical to irregularly expanded and up to 5 mm wide. Its inner margin is lined with distinct, papery teeth up to 3 mm long. The lid or operculum
Operculum (botany)
An operculum, in botany, is a term generally used to describe a structure within a plant, moss, or fungus acting as a cap, flap, or lid. In plants, it may also be called a bud cap.Examples of structures identified as opercula include:...
is ovate and may bear a small apical appendage on its lower surface. Up to 100 nectar glands are present on the underside of the lid. A spur
Spur (biology)
A spur in botany is a spike, usually part of a flower.In certain plants, part of a sepal or petal develops into an elongated hollow spike extending behind the flower, containing nectar which is sucked by long-tongued animals . Plants with such structures include Delphinium, Aquilegia, Piperia, and...
(≤5 mm long), which may be unbranched, bifid, or trifid, is inserted near the base of the lid.
Nepenthes rhombicaulis has a racemose
Raceme
A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...
inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
. The penducle
Peduncle (botany)
In botany, a peduncle is a stem supporting an inflorescence, or after fecundation, an infructescence.The peduncle is a stem, usually green and without leaves, though sometimes colored or supporting small leaves...
and rachis
Rachis
Rachis is a biological term for a main axis or "shaft".-In zoology:In vertebrates a rachis can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the rachis usually form the supporting axis of the body and is then called the spine or vertebral column...
both reach 20 cm in length, although the latter is usually shorter in female plants. Partial peduncles are two-flowered and lack bract
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
eoles. Sepal
Sepal
A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...
s are elliptical and up to 4 mm long.
Most parts of the plant are virtually glabrous. The margins of the lamina are often lined with short red hairs. Inflorescences may have a sparse indumentum
Indumentum
The indumentum is a covering of fine hairs or bristles on a plant or insect.In plants, the indumentum types are:*pubescent*hirsute*pilose*villous*tomentose*stellate*scabrous*scurfy...
of minute hairs.
The stem and lamina are green. Lower pitcher range in colour from dull green throughout to light red with purple blotches. The peristome may be light green to dark purple and is often darker around its outer margin. According to Schmid-Höllinger, upper pitchers are yellowish-green with pale red spots in the upper part and pitchers produced on offshoots
Offshoot (plant)
Offshoots are lateral shoots that are produced on the main stem of a plant. They may be known colloquially as "suckers". Also see basal shoot....
from the climbing stem have clear red speckles throughout.
Ecology
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
n province of North Sumatra
North Sumatra
North Sumatra is a province of Indonesia on the Sumatra island. Its capital is Medan. It is the most populous Indonesian province outside of Java. It is slightly larger than Sri Lanka in area.- Geography and population :...
, particularly around Lake Toba
Lake Toba
Lake Toba is a lake and supervolcano. The lake is 100 kilometres long and 30 kilometres wide, and 505 metres at its deepest point. Located in the middle of the northern part of the Indonesian island of Sumatra with a surface elevation of about , the lake stretches from to...
. Plants that appear to match the description of N. rhombicaulis have also been recorded from Mount Bandahara in Aceh
Aceh
Aceh is a special region of Indonesia, located on the northern tip of the island of Sumatra. Its full name is Daerah Istimewa Aceh , Nanggroë Aceh Darussalam and Aceh . Past spellings of its name include Acheh, Atjeh and Achin...
. The species is known with certainty only from the Mount Pangulubao
Mount Pangulubao
Mount Pangulubao or Pangulubau is a mountain near Lake Toba in Sumatra.Mount Pangulubao is notable for the relatively large number of tropical pitcher plant species that inhabit its forests. These include Nepenthes ampullaria, Nepenthes gymnamphora, Nepenthes mikei, Nepenthes ovata, Nepenthes...
complex and Mount Lubukraya, although Shigeo Kurata
Shigeo Kurata
is a Japanese botanist and Nepenthes taxonomist whose work in the 1960s and 1970s contributed much to the current popularity of these plants. Of particular note is his 1976 guide, Nepenthes of Mount Kinabalu....
suggested that it is likely to be more widespread in the Lake Toba region. Nepenthes rhombicaulis has an altitudinal distribution of 1600–2000 m above sea level.
Nepenthes rhombicaulis grows terrestrially in dense, shady montane forest. It is usually found in lower montane forest above steep slopes, but has also been recorded from upper montane forest. It is one of the few Nepenthes species that are common in the understory
Understory
Understory is the term for the area of a forest which grows at the lowest height level below the forest canopy. Plants in the understory consist of a mixture of seedlings and saplings of canopy trees together with understory shrubs and herbs...
.
Lower pitchers frequently develop embedded in detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
and leaf litter on the forest floor, resulting in their often deformed appearance. Bruce Salmon noted that lower pitchers which develop in this way grow around twice as large as those which develop completely above ground. He postulated that the species is adapted to trapping subterranean insects, although he did not examine the contents of these pitchers to test the hypothesis.
In its natural habitat, N. rhombicaulis occurs sympatrically with N. flava
Nepenthes flava
Nepenthes flava is a tropical pitcher plant endemic to northern Sumatra, where it grows in montane forest at 1800–2200 m above sea level....
, N. ovata
Nepenthes ovata
Nepenthes ovata is a tropical pitcher plant endemic to Sumatra. The specific epithet ovata is Latin for "ovate" and refers to the shape of the lower pitchers.-Botanical history:...
, N. spectabilis
Nepenthes spectabilis
Nepenthes spectabilis is a tropical pitcher plant endemic to Sumatra, where it grows at elevations of between 1400 and 2200 m above sea level. The specific epithet spectabilis is Latin for "visible" or "notable".-Botanical history:...
, and N. tobaica
Nepenthes tobaica
Nepenthes tobaica is a tropical pitcher plant endemic to Sumatra. It is particularly abundant around Lake Toba, after which it is named....
. Natural hybrids with all of these species have been recorded. On Mount Pangulubao, N. gymnamphora
Nepenthes gymnamphora
Nepenthes gymnamphora is a tropical pitcher plant native to the Indonesian islands of Java and Sumatra. There is much debate surrounding the taxonomic status of this species and the taxa N. pectinata and N. xiphioides....
(N. xiphioides) and N. mikei
Nepenthes mikei
Nepenthes mikei is a tropical pitcher plant endemic to Sumatra. It is characterised by its black mottled lower and upper pitchers. The species is closely related to N. angasanensis and N. tobaica....
grow around 100 m above populations of N. rhombicaulis.
Due to its somewhat restricted distribution, N. rhombicaulis is listed as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
on the 2006 IUCN Red List of Threatened Species
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
.
Related species
Nepenthes gymnamphora
Nepenthes gymnamphora is a tropical pitcher plant native to the Indonesian islands of Java and Sumatra. There is much debate surrounding the taxonomic status of this species and the taxa N. pectinata and N. xiphioides....
in both morphology and growth habit. It is sympatric with this species on Mount Pangulubao
Mount Pangulubao
Mount Pangulubao or Pangulubau is a mountain near Lake Toba in Sumatra.Mount Pangulubao is notable for the relatively large number of tropical pitcher plant species that inhabit its forests. These include Nepenthes ampullaria, Nepenthes gymnamphora, Nepenthes mikei, Nepenthes ovata, Nepenthes...
. Nepenthes rhombicaulis also bears a close resemblance to N. hirsuta
Nepenthes hirsuta
Nepenthes hirsuta , the Hairy Pitcher-Plant, is a tropical pitcher plant endemic to Borneo. It is characterised by an indumentum of thick brown hairs, which is even present on the inflorescence. Pitchers are mostly green throughout with some having red blotches on the inside surfaces.N. hirsuta...
from Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....
.
In 2001, Charles Clarke
Charles Clarke (botanist)
Dr. Charles M. Clarke is a botanist and taxonomist specialising in the carnivorous plant genus Nepenthes. Clarke has an honours degree in Botany from Monash University in Melbourne, and a Ph.D. in Ecosystem Management at the University of New England, in Armidale, New South Wales.Clarke first...
performed a cladistic analysis of the Nepenthes species of Sumatra and Peninsular Malaysia
Peninsular Malaysia
Peninsular Malaysia , also known as West Malaysia , is the part of Malaysia which lies on the Malay Peninsula. Its area is . It shares a land border with Thailand in the north. To the south is the island of Singapore. Across the Strait of Malacca to the west lies the island of Sumatra...
using 70 morphological characteristics of each taxon. The resultant cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
placed N. rhombicaulis in an unresolved polytomy
Polytomy
A polytomy , meaning many temporal based branches, is a section of a phylogeny in which the evolutionary relationships can not be fully resolved to dichotomies. In a phylogenetic tree, a polytomy is represented as a node which has more than two immediate descending branches...
at the base of the Montanae/Nobiles
Nepenthes classification
The taxonomy of Nepenthes has been revised several times during the nineteenth and twentieth centuries.-Nineteenth century:The first subgeneric division of the Nepenthes was made by Joseph Dalton Hooker in his 1873 monograph, "Nepenthaceae"...
clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, together with N. benstonei
Nepenthes benstonei
Nepenthes benstonei is a tropical pitcher plant endemic to Peninsular Malaysia, where it occurs at elevations of 450–600 m above sea level...
.
Natural hybrids
At least four natural hybrids involving N. rhombicaulis have been recorded and at least three of the parent species (excluding N. rhombicaulis) occur on Mount Pangulubao.- N. flavaNepenthes flavaNepenthes flava is a tropical pitcher plant endemic to northern Sumatra, where it grows in montane forest at 1800–2200 m above sea level....
× N. rhombicaulis - ? N. gymnamphoraNepenthes gymnamphoraNepenthes gymnamphora is a tropical pitcher plant native to the Indonesian islands of Java and Sumatra. There is much debate surrounding the taxonomic status of this species and the taxa N. pectinata and N. xiphioides....
× N. rhombicaulis - N. ovataNepenthes ovataNepenthes ovata is a tropical pitcher plant endemic to Sumatra. The specific epithet ovata is Latin for "ovate" and refers to the shape of the lower pitchers.-Botanical history:...
× N. rhombicaulis - N. rhombicaulis × N. spectabilisNepenthes spectabilisNepenthes spectabilis is a tropical pitcher plant endemic to Sumatra, where it grows at elevations of between 1400 and 2200 m above sea level. The specific epithet spectabilis is Latin for "visible" or "notable".-Botanical history:...
- N. rhombicaulis × N. tobaicaNepenthes tobaicaNepenthes tobaica is a tropical pitcher plant endemic to Sumatra. It is particularly abundant around Lake Toba, after which it is named....