During a visit to study Nepenthes in Indonesian New Guinea in June 2017,
a new species to science came to light that was published in early 2018
(Cheek et al. 2018). Formerly confused with N. insignis Danser, it is conﬁned
to limestone on the island of Biak off the north coast of New Guinea, and
consequently was named as Nepenthes biak Jebb & Cheek (Figs. 1 & 2).
Royal Botanic Gardens, Kew, TW9 3AE, U.K.
Michal R. Golos
School of Biological Sciences, University of Bristol, 24 Tyndall Avenue,
Bristol, BS8 1TQ, U.K.
Fig 1: The original line-drawing of Nepenthes biak from Cheek et al. (2018)
Limestone, being mostly pure calcium carbonate, and so highly alkaline, is
such a challenge for plant species that most do not thrive growing directly on
it. This is partly because salts and minerals, including iron and manganese,
are available only with difﬁculty due to the alkaline pH. Limestone is a
free-draining substrate, so in seasonal climates is more prone to drought
conditions than normal substrates. This can also pose a physiological
challenge for many plant species, so such substrates tend to have sparser
and shorter woody growth than neighbouring non-limestone areas. Most
plant species avoid limestone and so are known as calcifuges. But some
plant species are adapted to it and have evolved mechanisms for mineral
uptake on limestone. Plants that grow on limestone are known as calcicoles
and can be classiﬁed into two groups: facultative calcicoles are species which
can grow either on or off limestone, while obligate calcicoles are restricted
to limestone. Obligate calcicoles occur in many unrelated plant groups.
Several species of Pinguicula, for example, such as Pinguicula vallisneriifolia
Webb, are obligate calcicoles, entirely restricted to limestone. There are
advantages to species being able to grow on limestone: competition from
other plant species in such habitats is much lower, because most plant
species cannot survive or thrive on it. On the downside, obligate calcicoles
are restricted to limestone outcrops and cannot grow anywhere else. If
limestone areas are remote from each other, calcicole species may not be
able to spread to new sites. This has resulted in many calcicoles being
restricted to individual or closely neighbouring limestone patches.
In the Flora Malesiana account of Nepenthes (Cheek & Jebb 2001: 3), it
is remarked that obligate limestone species are only known from Borneo:
Nepenthes boschiana Korth. (now known also to occur on ultramaﬁc
substrate; Lee 2004), N. campanulata Sh.Kurata, N. faizaliana J.H.Adam
& Wilcock, N. mapuluensis J.H.Adam & Wilcock and N. northiana Hook.f.,
and that facultative limestone species are N. reinwardtiana Miq. and N.
albomarginata T.Lobb ex Lindl. (recorded on limestone in Borneo only). It
was considered strange that no Nepenthes had been reported from the
limestone outcrops of the Philippines, Sumatra or of New Guinea, possibly
due to under collecting.
Limestone areas are scattered throughout SE Asia, a legacy of its geological
origins: many of the islands are uplifted from the sea ﬂoor and so have
surfaces of accreted coral (i.e. limestone). Additional facultative limestone
species have been reported from Borneo by Lee (2004): N. ampullaria Jack,
N. gracilis Korth., N. lowii Hook.f., N. mirabilis (Lour.) Druce, N. stenophylla
Mast., N. tentactulata Hook.f., N. veitchii Hook.f., and N. vogelii Schuit. &
de Vogel. Additionally, N. epiphytica A.S.Rob., Nerz & Wistuba (Robinson et
al. 2011) has been described from two limestone peaks in eastern Borneo,
Fig 2: Photo of live Nepenthes biak from the Tropical Nursery, Kew. Photo by M. Cheek.
but from what little is known it appears to be strictly epiphytic.
In the last two decades, additional limestone species have come to light
from two areas outside Borneo:
The area of Peninsular Thailand just north of the border with Malaysia,
where several N–S ridges of limestone occur has yielded a trio of new
calcicoles. The ﬁrst of these limestone Nepenthes to be published was
Nepenthes thai Cheek (Cheek & Jebb 2009), followed by Nepenthes rosea
M.Catal. & Kruetr. (Catalano 2014) and most recently Nepenthes krabiensis
Nuanlaong, Onsanit, Chusangrach & Suraninpong (Nuanlaong et al. 2016).
These are the ﬁrst records of calcicoles in the Montanae section or species
group which extends from Java, through Sumatra and the Malay Peninsula.
Further south and east in the Raja Ampat islands, Biak and neighbouring
West Papua of Indonesian New Guinea, Nepenthes treubiana Warb.,
discovered over a century ago, has been found to be a limestone species.
It is not unusual as in this species, that in the initial description, substrate
is not mentioned. Nepenthes biak is the second calcicole described from
western New Guinea, but at least one other undescribed species exists
on limestone in the Raja Ampats (Cheek et al. 2018). Both these species
belong in the Insignes (Nepenthes ventricosa Blanco) group, previously
thought to be entirely restricted to the Philippines apart from N. insignis
Danser itself. Again, these records are the ﬁrst time that calcicole species
have been recorded in that group.
The absence of calcicole species from Sumatra is not surprising since most
of the limestone in that island occurs in the north, where the climate is more
seasonal and so Nepenthes diversity is very low. More surprising is the
near absence of such species from the Philippines, where despite many
new discoveries, only two limestone records are known to us. One of these
is Nepenthes viridis Micheler, Gronem., Wistuba, Marwinski, W.Suarez &
V.B.Amoroso (Micheler et al. 2013) from the Alatae, the largest and most
widespread of the Philippine species-groups. This plant very closely
resembles N. graciliﬂora Elmer, but is recorded from limestone in northern
Mindanao, so may yet be distinct, if so it may have evolved only recently.
The second is a record claimed to be Nepenthes campanulata (but still to
be conﬁrmed with a specimen) from that part of Palawan closest to Borneo
(Clarke et al. 2014). Considering the vast extent of the Philippine archipelago
and the multiple outcrops of limestone, the records of Nepenthes from that
country are puzzlingly minute compared with Borneo.
However, it may be that as with N. treubiana, the limestone substrate of one or
more species has not been recorded. It is likely that more limestone species
of Nepenthes will be found as exploration progresses. Yet limestone is a
dangerous substrate on which to depend, especially in the neighbourhood
of transport links and cities: it is the principle component of cement, crucial
to concrete for constructing large buildings and transport and industrial
infrastructure. Extensive areas of the substrate remain to be surveyed for
plants in New Guinea, and, surely, limestone there, in the Philippines, and
perhaps Sulawesi, will one day yield yet more calcicole Nepenthes.
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Magazine 36: 24–31.
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Leiden. 157 pp.
Cheek M, Jebb M. 2009. Nepenthes group Montanae (Nepenthaceae) in Indo-China,
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Cheek M, Jebb M, Murphy B, Mambor F. 2018. Nepenthes section Insignes in Indonesia, with
two new species. Blumea 62(3): 174–178. https://doi.org/10.3767/blumea.2018.62.03.03
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and distribution of Nepenthes in Southeast Asia. Plant and Soil 403(1–2): 37–51. https://doi.
Lee C. 2004. Nepenthes. In: Yong H, Ng F, Yen E (eds.). Sarawak Bau limestone biodiversity.
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Micheler M, Gronemeyer T, Wistuba A, Marwinski D, Suarez W, Amoroso V. 2013. Nepenthes
viridis, eine neue Nepenthes-Art von der Insel Dinagat, Philippinen. Das Taublatt 76: 4–21.
Nuanlaong S, Onsanit S, Chusangrach V, Suraninpong P. 2016. A new species
of Nepenthes (Nepenthaceae) from Thailand. Thai Forest Bulletin (Botany) 44(2): 128–
Robinson A, Nerz J, Wistuba A. 2011. Nepenthes epiphytica, a new pitcher plant from
East Kalimantan. In: McPherson S. New Nepenthes: Volume One. Redfern Natural History
Productions, Poole. pp. 36–51.