Nepenthes mollis

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 : 138-139

Relationship to Nepenthes mollis

Nepenthes fractiflexa is very closely allied to N. mollis , which, following the emended circumscription of Robinson et al. (2019), includes N. hurrelliana . Prior to the description of N. hurrelliana by Cheek et al. (2003), the northern populations of N. mollis were variously treated as the natural hybrid N. fusca [s.lat.] × N. veitchii ( Phillipps & Lamb 1988) , as N. veitchii (Anon. 1990) , or as an undescribed species ( Phillipps & Lamb 1996, Clarke 1997, Steiner 2002), though Salmon (1999) astutely noted—based only on the limited evidence available at the time—that they might be conspecific with N. mollis .

Lee (2004) and Phillipps et al. (2008) considered plants representing Nepenthes fractiflexa from Mt. Mulu and the Kelabit Highlands to fall within the natural variability of N. hurrelliana , the former proposing that the differences in stem morphology could be explained by ecological factors, with the long-decurrent petiolar wings of N. fractiflexa postulated to be expressed only in the shadier environs afforded by lower-elevation montane forest. This hypothesis is disproved by the exposed, high-elevation, ridgetop habitat of plants from Mt. Bagong and Mt. Lumut, which nonetheless have the characteristic stem of the other populations ( Fig. 6 ). Indeed, the known elevational ranges of the two species— 1400–2150 m for N. fractiflexa and 1300–2400 m for N. mollis (see Phillipps et al. 2008, Robinson et al. 2019)—are very similar.

When the Mt. Bagong population of Nepenthes fractiflexa was first documented in May 2018 by Chien Lee and Mathias Scharmann ( Lee 2018, Scharmann 2018b), and again in June 2018 by AR, the plants were recognised as conspecific with the Mulu specimens, but, owing to their general morphology and geographical proximity to the Kemul Massif, were initially considered to represent N. mollis s.str. (as distinct from N. hurrelliana ; Clarke 2018, AR pers. observ.). The subsequent discovery—on Batu Luye’u in the Kemul Massif on 07 July 2018 —of plants matching exactly the holotype of N. mollis made it clear that N. mollis was conspecific with N. hurrelliana , and that the specimens from Bagong and Mulu represented not N. mollis , but rather a closely related and hitherto undescribed species ( Robinson et al. 2019).

Nepenthes fractiflexa shares with N. mollis the general form of its pitchers and broadly decurrent petiolar wings (though in N. mollis their development varies even within populations, depending on growth phase, and they never span the length of the internode). N. fractiflexa is however a more diminutive and gracile plant in all respects, with markedly smaller upper pitchers and a less developed indumentum. It also differs in its growth habit and plant architecture, producing secondary stems with far greater frequency and often having activated axillary buds. The peristomes of both the lower and upper pitchers are much more developed in N. mollis , having larger teeth and ribs and being significantly larger in both relative and absolute terms. In intermediate pitchers in particular, it is not uncommon for the height of the peristome column to equal or even exceed that of the ascidium below the peristome (AR pers. observ.). By contrast, in N. fractiflexa the peristome is usually little more than half to two-thirds as tall as the ascidium beneath. The lid of N. mollis is also markedly broader, particularly in upper pitchers. A basal lid appendage is conspicuous in all pitchers of N. mollis but reaches its greatest development in the upper pitchers, where it is 4–6 mm long and often hook-shaped; the opposite is true in N. fractiflexa , with lower pitchers having a prominent basal appendage ( Fig. 4E ) and upper pitchers only a slight basal swelling ( Fig. 5C ). N. fractiflexa has unusually long partial peduncles that bifurcate medially; N. mollis is variable in this respect, the partial peduncles often being shorter and branching basally ( Cheek et al. 2003, Robinson et al. 2019), though they may also branch medially (see e.g., the specimens S. 80020 (Julaihi & Jemree) and S. 87447 (Lee & Jong), both SAR!).

Literature records for Nepenthes mollis (mostly reported as N. hurrelliana ) cover Brunei (Bukit Pagon; 1850 m), Kalimantan(two peaks within the Kemul Massif:Batu Luye’u at 2054 m and Mt.Kemul at 1847 m), Sabah (Mt. Lumarku [1966 m] and the Meligan Range near Long Pasia, including Mt. Rimau [ca. 1900 m]), and Sarawak (Batu Buli, Mt. Mulu, and Mt. Murud) ( Cheek et al. 2003, Phillipps et al. 2008, Lamb et al. 2009, Scharmann 2010a, 2010b, 2018 a, Robinson et al. 2019). While it cannot be stated definitively that N. mollis is absent from Mt. Mulu, all candidates examined so far appear to represent N. fractiflexa . The same is true of plants from Batu Lawi grown for some years in Australia (Greg Bourke pers. comm.). The supposed Batu Buli population, which naturally hybridises with N. chaniana and N. lowii , is somewhat atypical and has been referred to as N. aff. hurrelliana ( Scharmann 2010a, 2018a), but based on the photographs available to the authors—and particularly the lower pitcher wings and colouration of the pitcher body—it is considered likely to fall within the natural variation of N. fractiflexa , though the development of the peristome column is reminiscent of N. mollis in terms of its height. The presence of the latter species on Batu Buli or Batu Lawi would not be surprising given the peaks’ proximity to Mt. Murud, and further field studies are merited. The plants on Mt. Rimau include both N. mollis and a putative natural hybrid between N. mollis and N. zakriana (Melaga Lait pers. comm., 2019); the latter species has not been confirmed this far south previously (see Robinson et al. 2019: fig. 4). Additionally, verifiable localities for N. mollis known to the authors include: Mentarang Hulu (ca. 1600 m) in North Kalimantan, where it grows with N. lowii , N. tentaculata , and the little-known N. fusca s.str. (AL pers. observ., 2017); Mt. Lunjut (ca. 1850 m), also in North Kalimantan (Sidiyasa & Arifin 1544, L!); and Mt. Muruk Miau (2083 m) of the Meligan Range near Long Pasia in Sabah, which also hosts a putative hybrid with N. veitchii , a species N. mollis co-occurs with ( Hiew 1992, Maik Miki pers. comm., 2019).

The known distributions of Nepenthes fractiflexa and N. mollis tend south-westward and north-eastward, respectively ( Fig. 2 ). This pattern may perhaps reflect edaphic heterogeneity: of Bukit Pagon, Mt. Lumarku, Mt. Murud, the Meligan Range and the Kemul Massif—all known to harbour only N. mollis —the first four are sandstone formations, while the last is a chimaeric non-lateritic peak, whereas N. fractiflexa has been recorded exclusively from surface laterites (Batu Buli, Hose Mountains, and Mt. Bagong) or else as an epiphyte (Batu Lawi, Mt. Bagong, and Mt. Mulu) (AR, JDW, MB, MD pers. observ.; see Tate 2001, Hutchison 2005, Lamb et al. 2009). A hydrological cause seems unlikely given the parallel habitats of the two species. Indeed, since the distributions of N. fractiflexa and N. mollis are so incompletely known this apparent pattern may be wholly artefactual.

Figures

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 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.