''Nepenthes dubia'' is a tropical

pitcher plant Pitcher plants are several different carnivorous plants which have modified leaves known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of what are considered to be "true" pitcher p ...

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to the Indonesian island of Sumatra, where it grows at an altitude of 1600–2700 m above sea level. The specific epithet ''dubia'' is the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word for "doubtful".

Botanical history

''Nepenthes dubia'' was first collected on May 29, 1917 by H. A. B. Bünnemeijer on Mount Talakmau, at an altitude of around 1900 m above sea level. Eleven years later, B. H. Danser formally described ''N. dubia'' in his seminal monograph "

The Nepenthaceae of the Netherlands Indies "The Nepenthaceae of the Netherlands Indies" is a seminal monograph by B. H. Danser on the tropical pitcher plants of the Dutch East Indies and surrounding regions. It was originally published in the ''Bulletin du Jardin Botanique de Buitenzorg ...

". Danser noted similarities between ''N. dubia'' and the closely related '' N. inermis'' and suggested that it might represent a natural

hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...

involving this species. He wrote:

''N. dubia'' strongly resembles the striking ''N. inermis'', but the difference is too large to unite these two species. ''N. inermis'', like ''N. Lowii'' has only a rudiment of a peristome. ''N. dubia'' has a broad and flat one. There are, however, also differences in the other parts: the pitchers are less widely infundibuliform and the lid is not so narrow as in ''N. inermis''. Perhaps ''N. dubia'' is a hybrid of ''N. inermis'' and another species with normal peristome and in that case ''N. Bongso'' could be the other parent species, the more so as the vegetative parts of ''N. inermis'', ''N. dubia'' and ''N. Bongso'' are very similar, and between the other species of the ''gymnamphora''-group intermediate forms often occur.

Danser based his description on the specimen collected in 1917, ''Bünnemeijer 938''. It consists of a portion of a climbing stem with upper pitchers. The specimen is deposited at the

Bogor Botanical Gardens The Bogor Botanical Gardens ( id, Kebun Raya Bogor) is a botanical garden located in Bogor, Indonesia, 60 km south of central Jakarta. It is currently operated by Indonesian Institute of Sciences (Indonesian: ''Lembaga Ilmu Pengetahuan Ind ...

(formerly the Herbarium of the Buitenzorg Botanic Gardens) in

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...

and Herbarium Lugduno-Batavum in

Leiden Leiden (; in English and archaic Dutch also Leyden) is a city and municipality in the province of South Holland, Netherlands. The municipality of Leiden has a population of 119,713, but the city forms one densely connected agglomeration wi ...

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

. ''Bünnemeijer 938'' was later designated as the

lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...

of ''N. dubia'' by

Matthew Jebb Matthew Hilary Peter Jebb (born 1958) is an Irish botanist and taxonomist specialising in the ant plant genera ''Squamellaria'', '' Myrmecodia'', '' Hydnophytum'', ''Myrmephytum'' and '' Anthorrhiza'', as well as the carnivorous plant genus '' ...

and

Martin Cheek Martin Roy Cheek (born 1960) is a botanist and taxonomist at the Royal Botanic Gardens, Kew.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.Clarke, C.M. & C.C. Lee 2004. ''Pitcher Plants of Sarawak''. Natural History Publications (Borneo), ...

incorrectly identified specimens of a natural cross between ''N. inermis'' and '' N. talangensis'' as belonging to ''N. dubia''. Kurata would later describe this hybrid as a new species, '' N. pyriformis''. In 1986, Mitsuru Hotta and Rusjdi Tamin included plant material belonging to ''N. dubia'' and ''N. inermis'' in their description of '' N. bongso''. However, ''N. bongso'' differs considerably in pitcher morphology from these species and is not easily confused with them. In 1997,

and

Martin Cheek Martin Roy Cheek (born 1960) is a botanist and taxonomist at the Royal Botanic Gardens, Kew.A skeletal revision of ''Nepenthes'' (Nepenthaceae)", in which they referred to ''N. dubia'' specimens from Mount Talang (''Kurata s.n.'' SING) and the mountains of the Tjampo region near

Payakumbuh Payakumbuh ( Indonesian: Kota Payakumbuh, Minangkabau: Payokumbuah, Jawi: ) is the second largest city in West Sumatra province, Indonesia, with a population of 116,825 at the 2010 Census and 139,576 at the 2020 Census. It covers an area of 80 ...

(''Meijer 6949'' L). The latter specimen is the holotype of '' N. tenuis'', which Jebb and Cheek treated in synonymy with ''N. dubia''. However, subsequent authors have rejected this interpretation.

Charles Clarke Charles Rodway Clarke (born 21 September 1950) is a British Labour Party politician, who was the Member of Parliament (MP) for Norwich South from 1997 until 2010, and served as Home Secretary from December 2004 until May 2006. Early life T ...

restored ''N. tenuis'' to species rank in ''

Nepenthes of Sumatra and Peninsular Malaysia ''Nepenthes of Sumatra and Peninsular Malaysia'' is a monograph by Charles Clarke on the tropical pitcher plants of Sumatra, Peninsular Malaysia, and their minor surrounding islands. It was published in 2001 by Natural History Publications (Bor ...

'' (2001), citing differences in pitcher morphology. Clarke also identified ''Kurata s.n.'' as the natural hybrid ''N. × pyriformis'', which is similar to ''N. dubia'', but can be distinguished on the basis of several stable characters. The hybrid has a wider pitcher lid that is never relfexed beyond 90 degrees and the pitcher cup is not appressed in the lower parts as in ''N. dubia''. In addition, the mouth of ''N. × pyriformis'' is raised towards the back as opposed to being horizontal.

Description

''Nepenthes dubia'' is a climbing plant. The stem can reach 3 m in length and is 3 to 4 mm in diameter. It is cylindrical or slightly angular. Internodes are up to 10 cm long. Leaves are

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

and

coriaceous This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...

. The

lamina Lamina may refer to: Science and technology * Planar lamina, a two-dimensional planar closed surface with mass and density, in mathematics * Laminar flow, (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption betwee ...

lanceolate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular ...

spathulate This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...

in form. It may be up to 10 cm long and 2 cm wide. It has an acute apex and is gradually

attenuate In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at vari ...

towards the base, which clasps the stem for one third to a half of its circumference. Around three pairs of longitudinal veins are present on the lamina, originating from the basal third of the

midrib This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...

Pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in ...

veins are oblique and irregularly

reticulate Reticulation is a net-like pattern, arrangement, or structure. Reticulation or Reticulated may refer to: * Reticulation (single-access key), a structure of an identification tree, where there are several possible routes to a correct identificati ...

, although they are not easily distinguishable.

Tendril In botany, a tendril is a specialized stem, leaf or petiole with a threadlike shape used by climbing plants for support and attachment, as well as cellular invasion by parasitic plants such as '' Cuscuta''. There are many plants that have tend ...

s can be up to 15 cm long and may or may not have a curl. Rosette and lower pitchers are rarely produced. They are narrowly

infundibular An infundibulum (Latin for ''funnel''; plural, ''infundibula'') is a funnel-shaped cavity or organ. Anatomy * Brain: the pituitary stalk, also known as the ''infundibulum'' and ''infundibular stalk'', is the connection between the hypothalamus and ...

in the lower two-thirds, becoming ovoid above, and are sharply contracted below the rim. Terrestrial pitchers are relatively small, reaching 5 cm in height and 3.5 cm in width. A pair of fringed wings (≤3 mm wide) runs down the upper third of the pitcher beneath the rim. The glandular region covers the lower two-thirds of the inner surface. The pitcher mouth is round and slightly raised at the back. The

peristome Peristome (from the Greek ''peri'', meaning 'around' or 'about', and ''stoma'', 'mouth') is an anatomical feature that surrounds an opening to an organ or structure. Some plants, fungi, and shelled gastropods have peristomes. In mosses In mosse ...

is cylindrical, up to 3 mm wide, and bears indistinct teeth. The lid or operculum is ovate and slightly raised in the middle. It bears no appendages. An unbranched

spur A spur is a metal tool designed to be worn in pairs on the heels of riding boots for the purpose of directing a horse or other animal to move forward or laterally while riding. It is usually used to refine the riding aids (commands) and to ba ...

(≤4 mm long) is inserted at the base of the lid. Upper pitchers are generally larger, growing to 8 cm in height and 4 cm in width. They gradually arise from the ends of the tendrils, forming a 5 to 10 mm wide curve. They are tubular to infundibular in the lower parts with laterally appressed pitcher walls. As in ''N. inermis'', there is almost no gap between the walls in mature pitchers. The upper part of the pitcher is widely infundibular throughout. Wings are reduced to ribs in upper pitchers. The inner surface of the pitcher is covered with numerous small, slightly depressed glands, occurring at a density of 600-900 per square centimetre; it lacks a waxy zone. The pitcher mouth is ovate, horizontal, and acute towards the lid. It bears a cylindrical or

involute In mathematics, an involute (also known as an evolvent) is a particular type of curve that is dependent on another shape or curve. An involute of a curve is the locus of a point on a piece of taut string as the string is either unwrapped from or ...

peristome (≤4 mm wide) with indistinct teeth spaced 0.25 to 0.5 mm apart. The inner portion of the peristome accounts for around 45% 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. The lid is narrowly cuneate, without appendages, and up to 4 cm long and 0.7 cm wide. It is rounded at the apex, gradually attenuate towards the base, and bears numerous small round or elliptical glands on its undersurface. Characteristically, it is almost always reflexed beyond 180 degrees relative to the pitcher mouth. In upper pitchers, the unbranched spur is 3 to 5 mm long. ''Nepenthes dubia'' has a

racemose A raceme ( or ) or racemoid is an unbranched, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are produced as the s ...

inflorescence An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...

that is distinctly short and compact. The peduncle may be up to 8 cm long. The

rachis In biology, a rachis (from the grc, ῥάχις [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this c ...

grows to 10 cm in length, although it is usually shorter in female inflorescences.

Pedicel Pedicle or pedicel may refer to: Human anatomy *Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures ...

s are bracteolate and up to 8 mm long.

Sepal A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 The term ''sepalum'' was coine ...

s are oblong-lanceolate and up to 3 mm long. Most parts of the plant are virtually

glabrous Glabrousness (from the Latin '' glaber'' meaning "bald", "hairless", "shaved", "smooth") is the technical term for a lack of hair, down, setae, trichomes or other such covering. A glabrous surface may be a natural characteristic of all or part of ...

. Inflorescences sometimes bear a sparse

indumentum In biology, an indumentum (Latin, literally: "garment") is a covering of trichomes (fine "hairs") on a plant Davis, Peter Hadland and Heywood, Vernon Hilton (1963) ''Principles of angiosperm taxonomy'' Van Nostrandpage, Princeton, New Jersey, pa ...

of simple hairs.

Caducous Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part; structures that op ...

brown hairs are present on developing pitchers. The stem, inflorescence and tendrils are characteristically purplish-red in most plants. The lamina is green, often with a red midrib. Pitchers generally range in colour from light green to yellow throughout, although orange and red forms are also known to exist. Danser described the colour of herbarium specimens as "fallow-dun, here and there blackish".

Ecology

''Nepenthes dubia'' was for a long time thought to be

to Mount Talakmau, but it was recently found on a second mountain, where it grows at lower elevations of around 1600 m above sea level.McPherson, S.R. 2009. ''

Pitcher Plants of the Old World ''Pitcher Plants of the Old World'' is a two-volume monograph by Stewart McPherson on the pitcher plants of the genera '' Nepenthes'' and ''Cephalotus''. It was published in May 2009 by Redfern Natural History Productions and covers all species ...

''. 2 volumes. Redfern Natural History Productions, Poole. On Mount Talakmau, the species occurs at an altitude of 1800–2700 m. At lower elevations on Talakmau, it grows epiphytically in

montane forest Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...

. However, above around 2400 m, vegetation is very stunted and here ''N. dubia'' also grows terrestrially on clumps of moss.

In its natural habitat, ''N. dubia'' is sympatric with '' N. gymnamphora'', '' N. izumiae'', '' N. jamban'', and '' N. lingulata''. The stunted upper montane forest which these species inhabit is dominated by

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

s of the genera '' Dipteris'' and '' Dicranopteris''. Trees rarely exceed 3 m in height and few ''Nepenthes'' plants emerge above the vegetation. Due to its extremely localised distribution, ''N. dubia'' is listed as Critically Endangered on the 2006 IUCN Red List of Threatened Species. ''N. dubia'' occurs at several locations along the only permanent trail up Mount Talakmau. However, the upper pitchers of this species bear a peristome, and so are not as desirable as those of ''N. inermis''. Because of this, wild populations of ''N. dubia'' have not suffered from over-collection.

Carnivory

''Nepenthes dubia'' produces thick,

mucilaginous Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of ...

pitcher liquid similar to that found in related species such as '' N. inermis''. The pitchers of ''N. inermis'' function not only as pitfall traps but also as flypaper traps, with the sticky inner walls trapping flying insects above the surface of the fluid. A similar trapping method may be employed by ''N. dubia''. Nepenthes like '' N. jamban'' also use this method with

pitcher fluid.

Related species

''Nepenthes dubia'' belongs to a group of closely related montane Sumatran species that includes '' N. flava'',Wistuba, A., J. Nerz & A. Fleischmann 2007
flava'', a new species of Nepenthaceae from the northern part of Sumatra
''Blumea'' 52(1): 159–163. '' N. inermis'', '' N. jacquelineae'', '' N. jamban'',Lee, C.C., Hernawati & P. Akhriadi 2006
Two new species of ''Nepenthes'' (Nepenthaceae) from North Sumatra
''Blumea'' 51(3): 561–568. '' N. talangensis'', and '' N. tenuis''. These species are characterised by infundibular upper pitchers and highly viscous pitcher fluid. ''Nepenthes dubia'' is thought to be most closely related to ''N. inermis''. It shares with this species the general morphology of its pitchers and leaves. It differs in having a well-developed peristome, more glands on the underside of the lid, and the lid being reflexed by more than 180 degrees. The lid of ''N. dubia'' is unique in this respect and is almost always reflexed beyond this angle, unless surrounding objects prevent it from assuming such a position. In their description of ''N. tenuis'',

Joachim Nerz Dr. Joachim Nerz (born 1964) is a German taxonomist and botanist specialising in the carnivorous plant genera ''Heliamphora'' and '' Nepenthes''. Nerz has described several new species, mostly with Andreas Wistuba. Publications * Schlauer, J. ...

and

Andreas Wistuba Andreas Wistuba (born 4 March 1967) is a German taxonomist and botanist specialising in the carnivorous plant genera ''Heliamphora'' and '' Nepenthes''. More than half of all known ''Heliamphora'' species have been described by Wistuba. Pub ...

included a table of morphological characteristics that distinguish it from related species, including ''N. dubia'':Nerz, J. & A. Wistuba 1994
Five new taxa of ''Nepenthes'' (Nepenthaceae) from North and West Sumatra
. ''

Carnivorous Plant Newsletter The ''Carnivorous Plant Newsletter'' is the official publication of the International Carnivorous Plant Society (ICPS), the largest such organization in the world. It is headquartered in Walnut Creek, California. History and editorship The newsle ...

'' 23(4): 101–114.

In 2001,

performed a

cladistic analysis Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived chara ...

of the ''Nepenthes'' species of Sumatra and

Peninsular Malaysia Peninsular Malaysia ( ms, Semenanjung Malaysia; Jawi: سمننجڠ مليسيا), or the States of Malaya ( ms, Negeri-negeri Tanah Melayu; Jawi: نڬري-نڬري تانه ملايو), also known as West Malaysia or the Malaysian Peninsula, ...

using 70 morphological characteristics of each

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

. The following is part of the resultant

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

, showing "Clade 1", which has 51% bootstrap support. Its most strongly supported subclade is the sister pair of ''N. inermis'' and ''N. dubia'', having 95% support.Clarke, C.M. 2001. ''

''. Natural History Publications (Borneo), Kota Kinabalu.

Natural hybrids

A single mature female plant of ''N. dubia'' × '' N. izumiae'' grows along the summit trail on Mount Talakmau. It produces infundibular upper pitchers that are yellowish-green in colouration. The pitchers are relatively small, reaching only around 10 cm in height. As in ''N. dubia'', the stem and tendrils are purplish-red. The lamina is green with a red midrib. ''Nepenthes dubia'' × ''N. izumiae'' differs most obviously from ''N. dubia'' in having an ovate lid that is never reflexed beyond 180 degrees. This hybrid is listed as ''N. dubia'' × ''N. singalana'' in

's ''

'', since ''N. izumiae'' is very closely related to '' N. singalana'' and was only described as a distinct species in 2003.Clarke, C.M., T. Davis & R. Tamin 2003. ''Nepenthes izumiae'' (Nepenthaceae): a new species from Sumatra. ''Blumea'' 48(1): 179–182. In 2009, Adrian Y. Wartono observed a putative cross between ''N. dubia'' and '' N. jamban'' in an area where these two species grew with '' N. lingulata'' and '' N. rhombicaulis''. Among natural populations of '' N. jacquelineae'', botanist

observed a single plant that appears to represent a natural cross between ''N. dubia'' and ''N. jacquelineae''.

Notes

:a.Bünnemeijer reached the base of Mount Talakmau and set up camp there on April 21, 1917, at 400 m altitude. This was followed by a stay at 1060 m on the mountain's northwestern slope on May 6, at 1300 m on May 11, at 1900 m on May 21, and finally on the plateau, at an elevation of 2780 m, between June 1 and June 4, during which he climbed the summit.van Steenis-Kruseman, M.J., ''et al.'' 2006
Cyclopaedia of Malesian Collectors: H. A. B. Bünnemeijer
Nationaal Herbarium Nederland. :b.The original

description of ''N. dubia'' reads:

''Folia mediocria'' sessilia, lamina lanceolato-spathulata, nervis longitudinalibus utrinque c. 3, basi attenuata 1/3-2/3 caulis amplectente, vagina 0 ; ''ascidia rosularum'' et ''inferiora'' ignota ; ''ascidia superiora'' parva, parte inferiore tubulosa v. leviter ventricosa, supra medium infundibuliformia, costis 2 prominentibus ; peristomio fere horizontali, operculum versus acuto, applanato, 2-4 mm lato, costis 1/2-1/4 mm distantibus, dentibus 0 ; operculo anguste cuneato, facie inferiore plana ; ''inflorescentia'' ignota ; ''indumentum'' parcum, iuventute tomentum fuscum, denique deciduum.

References

External links

at the Carnivorous Plant Photofinder {{Taxonbar, from=Q293212 Carnivorous plants of Asia dubia Endemic flora of Sumatra Critically endangered flora of Asia Plants described in 1928 Taxa named by Benedictus Hubertus Danser