Nepenthes fractiflexa Golos, A.S.Rob. & Barer, 2020

Golos, Michal R., Robinson, Alastair S., Barer, Marc, Dančák, Martin, Witte, Jean De, Limberg, Adrien, Sapawi, Noorhana Binti Mohd & Tjiasmanto, Wewin, 2020, Nepenthes fractiflexa (Nepenthaceae), a new Bornean pitcher plant exhibiting concaulescent metatopy and a high degree of axillary bud activation, Phytotaxa 432 (2), pp. 125-143 : 127-137

Nepenthes fractiflexa Golos, A.S.Rob. & Barer , sp. nov. ( Figs. 1–6 ).

Type: — MALAYSIA. Borneo, Sarawak, Baram District, G. Mulu, path from Melinau Paku, 4800 ft [= 1463 m], 291 June 1961, Anderson 4508 (holotype SAR!, iso- K! 2).

− Nepenthes hurrelliana auct . non Cheek & A.L.Lamb [ Lee (2004: 98), partim [fig. 4]; Phillipps et al. (2008: 144), partim].

− Nepenthes sp. Bagong in Robinson et al. (2019: 100, fig. 2G).

Diagnosis: — Nepenthes fractiflexa differs from N. mollis in having climbing stems fractiflex (vs. ± straight), petiolar wings decurrent down entire internode (vs. ca. 1/5–1/3 of internode), axillary buds typically activated, forming large, bract-like prophylls 0.8–5 cm long (vs. dormant, nodular or slightly filiform), upper pitchers 10–17 cm tall with fine peristome ribs and teeth, basal appendage reduced to a slight swelling (vs. 18–24 cm tall with large ribs and teeth, basal appendage hook-shaped and 4–6 mm long), and inflorescences concaulescent, emerging from middle of internode, appearing adnate to stem (vs. emergent from leaf axils), with partial peduncles long and bifurcating medially (vs. shorter and usually bifurcating basally).

Description: —Epiphytic or terrestrial climbing to pendent shrub, to 2(–3) m tall. Stems of rosettes terete, 4–6 mm in diameter, internodes 0.5–3 cm long; vining stems ±terete, somewhat supple, 3–5 mm in diameter, often branching, with 0–4(–8) aerial secondary stems, fractiflex, internodes generally angled at ca. 15–30º to the central axis of the stem (ca. 120–150º between internodes), 8–12 cm long, axillary buds typically 1–3 mm above axil (those directly subtending inflorescence often considerably more distant from axil), often partially activated, subtended by 1–2(– 3) large, bract-like, ±subulate prophylls 0.8–5 cm long. Leaves of rosettes coriaceous, shortly petiolate, ±alternatepentastichous, lamina obovate, becoming narrowly obovate with increasing internode length, 8–14 cm long, 2.5–4 cm wide, apex obtuse, not peltate, base gradually to markedly attenuate into petiole, petiole canaliculate, 0.8–1.8 cm long, not winged, not decurrent, sheathing and amplexicaul for 4/5 of the stem circumference. Longitudinal veins 2, conspicuous, on either side of midrib parallel to outer edge of lamina. Pinnate veins numerous, reticulate, indistinct. Tendrils ca. 0.5–1.5 times longer than the laminae, without curl, attaching to pitchers laterally. Leaves of climbing stems coriaceous, initially similar to rosette leaves but with a petiole to 4 cm long, initially without wings, amplexicaul, sheathing stem for 3/5–4/5 its circumference; with transition from intermediate to upper pitchers, or activation of intermediate stem axillary buds, the laminae abruptly become oblanceolate to oblong-spathulate, 8–12(–15) cm long, 2–3.5 cm wide, apex obtuse to sub-acute, the base with pronounced wings 0.3–0.8 cm wide, strongly oblique at axil and decurrent for entire length of internode, sometimes continuing slightly into the preceding internode, subtending 1/3 of stem circumference, margins ±parallel and attenuating only towards previous axil, phyllotaxy ±alternatedistichous; aerial rosettes may occasionally revert to the unwinged, pentastichous form of basal growths. Tendrils ca. 1.5–2 times longer than laminae, typically with 1.5 curls, attaching to pitchers at rear. Lower pitchers sub-cylindric, 8–15 cm tall, 2–5 cm wide, fringed wings usually well developed, rarely vestigial and restricted to upper portion of ascidium, 1–3(–5) mm wide with fringe elements (2–)5–8(–13) mm long, 2–6 mm apart; peristome slightly raised to ±horizontal at front of pitcher between wings, thereafter moderately oblique, becoming vertical in the rear third and typically recurved over pitcher opening towards lid, sub-cylindric at the front, 2–5 mm wide, rear part broader

1 The SAR and K specimens each bear an identical pair of labels that give two conflicting collection dates: 29 and 30 June. However, since there is just one plant on each sheet, they must have been collected on a single day.

2 SAR exsiccatum: climbing stem with three mature upper pitchers bearing lids, male inflorescence; K exsiccatum: climbing stem with mature lidless upper pitcher and developing upper pitcher, separate male inflorescence.

and slightly flattened, up to 3.5 times wider than at front, usually without marginal lobes, typically 1 lobe if present, ribs pronounced, 0.3–0.7 mm apart, teeth 0.3–0.6 mm long. Lid ovate, ±complanate, base subcordate, apex obtuse to retuse, 2–4 cm long, 1.2–2.6 cm wide, with pronounced abaxial midline rib and a semicircular basal keel, projecting 2–5 mm below lid, a filiform apical protuberance up to 2 mm may be present, with some variation even within single individuals. Spur simple, rarely fasciculate with ca. 3 branches, filiform, 3–7 mm long. Intermediate pitchers narrowly infundibuliform in the lower third, subcylindric to wholly infundibuliform above, typically widening from base to apex, 8–15(–18) cm long, 2.5–5 cm wide, fringed wings vestigial in the upper third, (0–) 1–2 mm wide, fringe elements 2–4(–7) mm long, 2–5 mm apart, or reduced entirely to prominent ridges; peristome slightly raised to ±horizontal between wings, front 1/2 near horizontal, abruptly becoming vertical in the rear 1/2 to 1/3, forming a column 3–6 cm tall, peristome 3–7 mm wide at front of pitcher, sub-cylindric, the raised, rear part somewhat flattened, up to 3.5 times wider than at front, outer edge slightly 2–3-lobed. Lid ovate with a cordate base, 2.5–4.5 cm long, 1.8–2.8 cm wide, apex obtuse, lower surface with reduced semicircular basal keel projecting 1–3 mm below lid, abaxial surface of lid with minute, thinly scattered glands, apical protuberance reduced, if present ±umbonate-conic, to ca. 2 mm long, 1 mm in diameter. Spur simple, filiform, 0.7–1 cm long, slightly recurved. Upper pitchers tubulose in the lower third and infundibuliform above or narrowly to broadly infundibuliform throughout, 10–17 cm long, 3–5.5 cm wide just below the mouth, often slightly constricted just below peristome, sometimes with appreciable ventral gibbosity, pitcher hollow continuing throughout curved basal portion and for some distance up to tendril, wings reduced to prominent ridges; form of peristome similar to intermediate pitchers, but 3–6 mm wide at front of mouth, the rear, flattened part only up to 2 times wider than at front and usually slightly more cylindric, column 2.5–4.8(–6) cm tall, often recurved over mouth at an angle of ca. 15–30° from vertical, ribs ±pronounced, 0.3–0.7 mm apart, 0.1–0.2(–0.4) mm high, teeth ca. 0.2 mm long at front of pitcher, generally becoming rounded and indistinct on column, rarely pointed and to ca. 0.5 mm long. Lid narrowly elliptic, 3.5–4.5 cm long, 0.8–1.8 cm wide, held at a large angle to the mouth, often almost vertically, margins recurved, sometimes undulate, midline rib prominent, basal keel reduced to a swelling, rarely projecting 1–2 mm below lid, apical appendage usually absent, if present as per intermediate pitchers. Inner surface predominantly to almost entirely glandular. Spur simple, filiform, up to 15 mm long. Inflorescences ±emergent from middle of internode, 3–5 cm above axil, appearing adnate to stem. Male inflorescence 18–22 cm long, 70–120 flowers, peduncle 4–7 cm long, 3–4 mm in diameter at the base, rachis 12–15 cm long, partial-peduncles 2-flowered, bifurcating ±medially, (2–) 5–8 mm from the base, bracts absent, pedicels 6–10(–18) mm long, tepals green becoming flushed with red after opening, elliptic, ca. 3.5 mm long, 2.5 mm wide, somewhat concave, adaxial surface with numerous pitted glands, apex rounded to acute; staminal column 3.2–4.2 mm long, anther head 1.5 mm in diameter, thecae and pollen grains whitish-yellow. Female inflorescence known only from a single spent example from the Hose Mountains; ca. 50 cm long, ca. 80 flowers, peduncle ca. 22 cm long, ca. 4–5 mm in diameter at the base, rachis ca. 28 cm long, partial-peduncles 2-flowered, bifurcating ca. 12–15 mm from the base, bracts absent, pedicels ca. 10 mm in length. Indumentum of coarse, brown to rufous hairs 0.8–1.5 mm long covering developing and young foliage, particularly the stem, leaf margins, the abaxial leaf surface, the abaxial midrib and the tendril, as well as more sparsely on the exterior surface of the pitchers, including the adaxial surface of the lid. This indumentum is variably caducous and may be lost from all parts in time, except for the abaxial surface of the laminae and midrib, the tendrils, and the pitchers. The indumentum of the adaxial leaf surface differs in being covered with short, simple, whitish hairs. Inflorescence indumentum poorly known, but seemingly caducous from the male inflorescence, with patchy remnants observed on specimens examined. Colour of mature stems usually a dark olive green, adaxial surface of laminae and petiole wings developing a brownish-bronze hue in bright light, lower pitchers dark olive through to bright green, sometimes blotched with deep red or purple, peristome base colour green, purple or red, contrastingly striped with yellow, red or green, upper pitchers usually uniformly yellowish-green, occasionally with large red to maroon flecks or, more rarely, granular brown mottling throughout (Batu Lawi), peristome yellow to beige with irregular reddishbrown striations, adaxial lid surface generally having similar pigmentation to pitcher exterior, sometimes with addition of reddish blotches, abaxial surface variably and prominently flecked with red.

Etymology: —The epithet fractiflexa is derived from the Latin words fractus (= broken) and flexus (= bend), and refers to the characteristic distichous vining stems of this species, which bend alternately at the nodes in a zig-zag fashion.

Phenology: —Male anthesis has been observed in the months of May on Mt. Bagong ( Scharmann 2018b) and June on Mt. Mulu (Anderson 4508). A recently spent male inflorescence was seen in January near Bukit Batu Buli (MD pers. observ.) and a spent female inflorescence was recorded in July in the Hose Mountains (MB pers. observ.).

Distribution: — Nepenthes fractiflexa has been documented over a wide area across central and eastern Sarawak and north-central Kalimantan ( Fig. 2 ). In the Kelabit Highlands it is known from the vicinities of Bukit Batu Lawi (JDW pers. observ., 2003) and Bukit Batu Buli (MD pers. observ., 2008 and 2009). Other sites in Sarawak include Mt. Mulu (AR & Brian Quinn pers. observ., 2014) and the Hose Mountains (MB pers. observ., 2016). In Kalimantan it has been recorded from Mt. Bagong (AR pers. observ., 2018) and two peaks near Punan Mahkam (AL pers. observ., 2019). Taken together, these peaks cover an area of some 45,000 km 2, though only a small number of plants have been recorded at each site. The species is known from an elevational range of 1400–2150 m a.s.l.

Given the known distribution of Nepenthes fractiflexa , it would not be unreasonable to infer its possible occurrence on a number of peaks between Mt. Bagong and the Hose Mountains, including Batu Jumak (ca. 2230 m) in North Kalimantan [though preliminary investigations have revealed only N. dactylifera A.S.Rob., Golos, S.McPherson & Barer in Robinson et al. (2019: 106), N. lowii Hooker (1859: 420) , and N. tentaculata Hooker (1873: 101) ; MD pers. observ.], as well as many of the high peaks along the Kalimantan– Sarawak border ( Fig. 2 ), particularly Batu Tiban (ca. 2025 m), Mt. Batubulan (1808 m), Mt. Panjang (ca. 1930 m), and a peak of uncertain name in the Iran Range of central Borneo (ca. 1898 m; Fig. 2 ).

Habitat and ecology: — Nepenthes fractiflexa grows both terrestrially and epiphytically in ridge forest and has most often been found as a ruderal species, populating suitable areas of disturbance, such as mountain tracks. The relative paucity of records might suggest that this species is, in natural conditions, predominantly a high epiphyte of tree limbs, the observations made in disturbed areas representing a sampling bias resulting from the ease of access that such sites offer.

The type population on Mt. Mulu (2376 m) is the most commonly encountered (see Lee 2004, Bourke 2007, 2010, 2011, Phillipps et al. 2008, Maerten 2016, Matschke 2018). There, the species has been recorded as an epiphyte at ca. 1400 m a.s.l. on the Melinau stream trail (AR pers. observ., 2014). In 2014 only three plants were observed ( Figs. 3A , 4A–C , 5A–B ), though more have been found since (see Maerten 2016, Matschke 2018). They were not sympatric with any other Nepenthes , though N. vogelii Schuiteman & de Vogel (2002: 537) grew within 200 m elevation (AR pers. observ.). Lee (2004) and Phillipps et al. (2008) noted vertical stratification of the Nepenthes species on Mt. Mulu, with N. dactylifera recorded [under the name N. fusca Danser (1928: 288) ] below 1200 m; N. vogelii at 1200–1500 m; and N. fractiflexa [as N. hurrelliana ] above 1500 m. The observed habitat on Mulu agrees with the herbarium label of the N. fractiflexa type specimen (collected from the same area), which records the habitat as “submontane (heath) forest”. Only a single small rosette plant (probably some 3 years old; Fig. 4A ) was recorded at the Mulu site (AR pers. observ.). This might deceptively suggest that recruitment is low, however only the small area adjacent to the track was explored and epiphytic seedlings are easily obscured by tree limbs.

The nearest known plants to the type population on Mt. Mulu were observed in the vicinity of Mts. Batu Buli (2082 m) and Batu Lawi (2046 m) in the Kelabit Highlands. Two mature specimens, including a male vining plant ( Fig. 5C ), were found at nearly 1900 m a.s.l. on the Tamu Abu ridge near Batu Buli, in open mossy forest consisting of stunted trees only a few metres tall (MD pers. observ., 2009). Several epiphytic rosette plants ( Fig. 4D–E ) were also photographed earlier at the same locality (MD pers. observ., 2008). Nepenthes chaniana Clarke, Lee & McPherson (2006: 56) , N. lowii and N. tentaculata grew nearby. A further observation of N. fractiflexa was made in the form of a single epiphytic plant ( Fig. 5D ) growing on a fallen tree at ca. 1600 m on the path from Pa Ukat to Batu Lawi, around 3 km from the summit of the latter (JDW pers. observ., 2003). This specimen is notable for its brown-stippled upper pitchers. In the vicinity grew N. chaniana , N. stenophylla Masters (1890: 240) , and N. veitchii Hooker (1859: 421) . An unconfirmed observation of the same taxon was additionally made near Ba’kelalan (on the eastern side of Mt. Murud) at a lower elevation (JDW pers. observ.).

Lying some 250 km southwest of the aforementioned sites, a single terrestrial plant ( Figs. 3B–C , 5E ) was found in the Hose Mountains, at the side of a logging road between Bukit Batu (2006 m) and Bukit Salong (ca. 1860 m), at 1550 m (MB pers. observ., 2016). A female scrambling vine with numerous secondary stems, it grew among Dicranopteris linearis ( Burman 1768: 235) Underwood (1907: 250) ferns on exposed clay laterite. The prey assemblage of the upper pitchers appeared to consist almost exclusively of ants, which were caught in large numbers. It grew in close proximity to, and at approximately the same elevation as, a large number of other Nepenthes , including N. appendiculata Chi. C.Lee, Bourke, Rembold, W.Taylor & S.T.Yeo in Lee et al. (2011: 24), N. chaniana , N. dactylifera , N. glandulifera Lee (2004: 95) , N. platychila Lee (2002: 257) , N. tentaculata , and N. veitchii . N. ephippiata Danser (1928: 286) was found some 200 m higher near the top of an adjacent peak (MB pers. observ.).

The first population of Nepenthes fractiflexa discovered outside of Sarawak was that on Mt. Bagong (ca. 2165 m), on the border between East and North Kalimantan, where the species has been observed at the side of the logging road that ascends to and cuts through the summit area (AR pers. observ., 2018; Figs. 3D , 4F , 5F , 6 ). This population grows mainly terrestrially, in humus overlying clay and sand, or in moss pads, at 1850–2150 m a.s.l., though mostly above 2000 m on summit ridges, making this the highest-elevation population known. At around a dozen individuals it is also the largest recorded thus far. The species grows in close proximity to N. lowii , and an isolated individual of N. dactylifera was also found growing nearby.Other species recorded from the mountain include N. chaniana , N. hirsuta Hooker (1873: 99) , N. reinwardtiana Miquel (1852: 168) , and N. tentaculata ( Robinson et al. 2019) , but these were not found close to the population of N. fractiflexa . Nematoceran flies have been observed visiting the peristomes of upper pitchers (see Clarke 2018). Explorations of peaks in the vicinity of Punan Mahkam, Berau Regency, East Kalimantan, have revealed two further localities for N. fractiflexa : Mt. Guguang (also known to the local Dayak Punan people as Mt. Gay; ca. 1450 m), where the species grows with N. dactylifera and N. reinwardtiana ; and Mt. Lumut (ca. 1470 m), where it grows with the two aforementioned species plus N. hirsuta (AL pers. observ., 2019). These plants notably have richly coloured upper pitchers.

Despite growing alongside numerous other Nepenthes species, no natural hybrids involving Nepenthes fractiflexa have been observed with certainty, though an unusually bulbous upper pitcher photographed on Mt. Mulu (Boon Leng pers. comm.) might indicate a cross with N. vogelii , which grows at slightly lower elevations nearby. Similarly, a rosette plant observed among putative N. fractiflexa plants at a disturbed site along an old logging road near Batu Buli (MD pers. observ.) might represent a hybrid with either N. chaniana or N. stenophylla , both of which are found in the area. A natural hybrid with N. lowii may also have been observed in the same area (see Discussion).

Conservation status:— Data available for Nepenthes fractiflexa are not currently sufficient to properly assess its geographic range, population size, or population dynamics. The seven recorded localities cover an area of about 45,000 km 2 (EOO) that encompasses dozens of peaks of suitable elevation that have yet to be botanised or even explored. It is therefore likely that the species has a considerably wider distribution than currently appreciated.

Out of the seven known populations of Nepenthes fractiflexa , at least one (the type population) is found within a national park, namely Gunung Mulu National Park in Sarawak. Additionally, the populations found near Batu Buli and Batu Lawi may grow in Pulong Tau National Park (in Sarawak), which encompasses Mt. Murud (2423 m) and whose boundary lies very close to these two mountains. The species is also likely to be present in the large Kayan Mentarang National Park (in North Kalimantan), which runs along the border with northeastern Sarawak and southwestern Sabah. However, while Nepenthes fractiflexa has a reasonably large distribution area, its currently known AOO is very small, as is the number of recorded locations and individuals. Taken together, these factors lead us to assess it as Near Threatened (NT) according to IUCN stipulations for the allocation of the NT category ( IUCN 2012).

Notes: —The authors are not aware of any herbarium material of Nepenthes fractiflexa other than the two type sheets reported in the present paper, plus a single specimen from the Kelabit Highlands (S. 87439 (Lee); see “Additional specimens examined”). This paucity of collections reflects the rarity with which this species is encountered in nature. N. fractiflexa seems only to have been unambiguously described and figured by Lee (2004, as N. hurrelliana ) and by Robinson et al. (2019, as ‘ N. sp. Bagong’). With the sole exception of Phillipps et al. (2008), who provide a condensed account of the Mulu population as presented by Lee (2004), N. fractiflexa is not mentioned in the major Nepenthes monographs or field guides covering its native range (i.e., Phillipps & Lamb 1988, 1996, Jebb & Cheek 1997, Clarke 1997, Cheek & Jebb 2001, Clarke & Lee 2004, McPherson 2009, McPherson & Robinson 2012), and has only previously appeared with certainty in a small number of online sources (e.g., Dančák 2009). This being the case, it is possible that some, if not all, literature records of N. hurrelliana from Batu Buli and Mt. Mulu actually represent N. fractiflexa (see Discussion). In particular, a rosette pitcher photographed by Greg Bourke on Mt. Mulu that appeared in a number of publications identified as N. hurrelliana is likely to represent N. fractiflexa (see Bourke 2007: 1 fig., Bourke 2010: fig. 7, Bourke 2011: fig. 10).

Although most of the observed Nepenthes fractiflexa plants have been terrestrial, all of these were growing in ruderal sites and the species is presumed to be predominantly epiphytic like its closest relatives. The observed skew towards terrestriality is therefore likely the result of sampling bias. This would explain why it is so seldom seen despite being widespread across north-central Borneo; the same is true of the closely allied but relatively more common N. dactylifera , N. vogelii , and N. zakriana ( Adam & Wilcock 1998: 151) Adam & Hamid (2006: 434) , as well as the little-known N. epiphytica Robinson, Nerz & Wistuba (2011: 36) from East Kalimantan (see Clarke 2001b, Clarke & Lee 2004, Phillipps et al. 2008, Robinson et al. 2011).

Additional specimens examined:— Nepenthes mollis (including N. hurrelliana ): BRUNEI: Gunong Pagon Priok, 5700 ft [= 1737 m], 20 October 1984, Cantley s.n. (K! [3 sheets]) [separate lower pitchers; lower pitcher with leaf, rosette with lower pitcher; lower pitcher with leaf fragment; “Under canopy, collection from diff. plants, epiphytic to 50’ [= 15 m]”]. KALIMANTAN: W. Koetai, [G.] Kemoel, [near Endert camp] 39 [of 1925 Midden-Oost-Borneo Expeditie; see ICWO ca. 1926, Buijs et al. 1927], ± 1800 m, 17 October 1925, Endert 4282 (holotype of N. mollis BO !) [pitcherless climbing stem with male inflorescence; single sheet labelled “Unicum!”]; East Kalimantan, Kab. Bulungan, Gunung Lunjut, Kayan Mentarang National Park, 2°36’N 115°35’E, 1400 m, 5 March 1999, Sidiyasa & Arifin 1544 (L!, WAN!) [L, WAN—stem with intermediate pitcher; “Stony area, on ridge. Sacs with mixed dark red and green colour.”]. SABAH: northeast Sarawak [sic!], Gunung Lumarku, 03°N 115°E [sic!], 1800 m, August 1996, AK 230972 (Salmon) (AK n.v., K!) [K—climbing stem with upper pitcher and male inflorescence; originally identified as “ Nepenthes? mollis ”; paratype of N. hurrelliana ; “Growing on mossy pads at the base of trees or epiphytically, along summit ridge. Few scattered plants at location. Up to 5 m tall. Occasionally lacking upper pitchers. Smaller pitchers from forest floor, larger ones from higher up. Specimen over 2 sheets AK 230972 & AK 230973.”]; S. Sabah, Gunung Luma[r]ku, 1700 m, 8 June 1995, Hurrell s.n. (K!) [stem with intermediate pitcher; “epiphytic, moss forest”; annotated N. “hurrellii”; labelled as paratype of N. hurrelliana but not cited in protologue; lamina sampled for phylogenomic analysis of Murphy et al. (2020) but DNA too fragmented to obtain useable sequence data (Bruce Murphy pers. comm.)]; G. Lumarku, no elevation data, August 1999 [per Cheek et al. 2003], Lamb & Surat 145/99 (holotype of N. hurrelliana SAN n.v., iso- K!, photo BO, SAN,?SING) [K—climbing stem with male inflorescence, separate upper and rosette pitchers]. SARAWAK: Gunong Murud, Summit Ridge, 2200 m, 22 March 1999, S. 80020 (Julaihi & Jemree) (SAR!) [climbing stem with upper pitchers, male inflorescence; “Montane [f]orest. Climbing to 1 meter high. Stem green with den[s]e brown hair. Leaves green with brown hair. Tendril brown. Pitcher green with brown hair. Lid small, triangular, green. Lip with purple and green stripes. Peduncle, pods brown.”]; Limbang, Gunung Murud, 3°56’01”N 115°31’77”E, 2129 m, 24 August 2005, S. 87447 (Lee & Jong) (SAR!) [pitcherless climbing stem with male inflorescence; “Mossy forest. Epiphytic plant growing c. 5 m up in fork of tree. Climbing vine hanging with no pitchers for terminal 1 m of vine. Lower pitchers growing from rosette at base of plant. Lower pitcher containing only 2 phasmid stick insects as prey.”].

Notes on specimens examined: — The collector of the Nepenthes fractiflexa type material, James Aidan Robb Anderson (1922–2004), recorded on its herbarium label: “Climbing pitcher plant in submontane (heath) forest. Pitchers in crown of Quercus at height of 50’ [= 15 m].” The live pitcher colour recorded by Anderson (“greenish, tinted with pale purple”) agrees with plants seen in the same area by AR and Brian Quinn ( Figs. 4C , 5A ). The vernacular name is given as tujud, but this word is not recognised today by speakers of the two local languages—Berawan and Penan— and has an unrelated meaning in Malay ; it was either transcribed incorrectly or represents a transient and extremely localised colloquial name with no extant currency.

The enduring uncertainty over the identity of this taxon is reflected in the numerous re-assignments recorded on the holotype at SAR: initially identified simply as an indeterminate Nepenthes species on Anderson’s original herbarium labels (one later turned into “ Nepenthes cf. maxima ” by an unknown hand), it was subsequently identified as a species similar to, but distinct from, N. fusca by M. Hotta (March 1967); as N. fusca by M. Cheek (1996); and as N. hurrelliana by C. Lee (19 February 2004). The K specimen (isotype) was similarly assigned to N. fusca s.lat. by an unknown author. Though the only mature pitcher on the isotype is missing its lid, a second, developing pitcher bears a (still sealed) lid matching those of the plants observed in habitat, while the leaves and stem of the specimen—including its exceptionally long axillary prophylls—otherwise unmistakably represent N. fractiflexa . The male inflorescence of the isotype is separated from the rest of the material, but its extremely long pedicels and partial peduncles are likewise congruent with field observations.

Lee (2004) cites a third sheet— S. 87439 (Lee), from the Kelabit Highlands —as having the same morphological features as observed in the Anderson material from Mulu. This specimen, collected on 12 October 1997 from the trail to Batu Lawi at 1600 m, is very likely to represent Nepenthes fractiflexa , but an extensive search of the collections at SAR in 2019 failed to locate it.

Figures

FIGURE 1. Nepenthes fractiflexa Golos, A.S.Rob. & Barer.A) portion of climbing stem with emerging inflorescence. B) upper pitchers, left ventral view, right lateral view. C) rosette pitcher. D) adaxial detail of a climbing stem leaf showing leaf venation and bract-like prophyll. E) climbing stem bearing upper pitchers and male inflorescence; note fractiflexion of stem. F) inflorescences, above male, below female. G) male flowers. H) detail of upper pitcher lid. I) detail of lower pitcher lid. Based on Anderson 4508 and supplemented with photographs and measurements made of in situ material. Illustration by M. Barer.

FIGURE 2. Distribution of Nepenthes fractiflexa and N. mollis in Borneo based on accessions held at BO, K, L, SAR and WAN herbaria, supplemented by field observations. Records of N. mollis (as N. hurrelliana) from Batu Buli, Batu Lawi and Mt. Mulu are omitted due to doubts over their identity (see Discussion). Drawn by A.S. Robinson.

FIGURE 3. Architecture and stem morphology of N. fractiflexa. A) plant entering climbing phase, with late-stage lower pitcher (Mt. Mulu); note fractiflex stem and spontaneous development of petiolar wings towards top-right. B) multi-branched stem (ca. 3 m long) trailing among Dicranopteris linearis ferns (Hose Mountains); note exposed clay laterite. C) detail of the same scrambling vine (Hose Mountains). D) distal end of climbing stem (Mt. Bagong); note dense pubescence. Photographs by B.D. Quinn (A), M. Barer (B, C), and A.S. Robinson (D).

FIGURE 4. Rosette and lower pitchers of N. fractiflexa. A) young rosette pitcher (Mt. Mulu). B) older rosette pitcher (Mt. Mulu). C) latestage lower pitcher (Mt. Mulu). D) hanging lower pitchers of two epiphytic rosettes (Batu Buli). E) recently opened lower pitcher (Batu Buli). F) rosette pitcher (Mt. Bagong); note reduced ventral wings and fasciculate spur. Photographs by B.D. Quinn (A, B), A.S. Robinson (C, F), and M. Dančák (D, E).

FIGURE 5. Aerial pitchers of N. fractiflexa. A) intermediate pitcher (Mt. Mulu); note similarity in colouration to lower pitchers. B) upper pitcher produced on a different shoot of the same plant (Mt. Mulu). C) upper pitcher (Batu Buli); note undulate lid margins and basal swelling on abaxial lid surface. D) upper pitcher (Batu Lawi); note brown stippling. E) upper pitcher (Hose Mountains). F) upper pitcher (Mt. Bagong). Photographs by B.D. Quinn (A, B), M. Dančák (C), J. De Witte (D), M. Barer (E), and A.S. Robinson (F).

FIGURE 6. Nepenthes fractiflexa growing in mossy forest on Mt. Bagong. The characteristic climbing stem (complete with spent male inflorescence) is visible in the background. Note the long-decurrent petiolar wings and large axillary prophylls. The orange pseudobulb adjacent to the foreground pitcher is that of a Dendrochilum sp. (Orchidaceae). Photograph by A.S. Robinson.