Wednesday, July 6, 2016

[Botany • 2016] Pittosporum peridoticola • A New Ultramafic Obligate Species (Pittosporaceae) restricted to Kinabalu Park (Sabah, Malaysia)

Pittosporum peridoticola 
 J.B.Sugau & Ent
Fig. 1 Pittosporum peridoticola in the field: (a) Habit of plant growing on ultramafic bedrock; (b) Whole plant; (c) Inflorescence; (d) Detail of inflorescence.
Photos by A. van der Ent and R. van Vugt DOI:  10.1186/s40529-016-0119-9


Kinabalu Park, in Sabah (Malaysia) on Borneo Island, is renowned for the exceptionally high plant diversity it protects, with at least 5000 plant species enumerated to date. Discoveries of plant novelties continue to be made in Sabah, especially on isolated ultramafic outcrops, including in the genus Pittosporum (Pittosporaceae) with P. linearifolium from Bukit Hampuan on the southern border of the Park, and P. silamense from Bukit Silam in Eastern Sabah, both narrow endemics restricted to ultramafic soils.

A distinctive new species of Pittosporum (Pittosporum peridoticola J.B.Sugau and Ent, sp. nov.) was discovered on Mount Tambuyukon in the north of Kinabalu Park during ecological fieldwork. The diagnostic morphological characters of this taxon are discussed and information about the habitat in which it grows is provided. The soil chemistry in the rooting zone of P. peridoticola has high magnesium to calcium quotients, high extractable nickel and manganese concentrations, but low potassium and phosphorus concentrations, as is typical for ultramafic soils. Analysis of foliar samples of various Pittosporum-species originating from ultramafic and non-ultramafic soils showed a comparable foliar elemental stoichiometry that is suggestive of ‘Excluder-type’ ecophysiology.

Pittosporum peridoticola is an ultramafic obligate species restricted to Kinabalu Park with only two known populations within the boundaries of the protected area. It is vulnerable to any future stochastic landscape disturbance events, such as forest fires or severe droughts, and therefore its conservation status is ‘Near Threatened’.

Keywords: Hyper-endemic; Mount Tambuyukon; Soil chemistry; Ultramafic obligate

Etymology: The specific epithet “peridoticola” denotes the peridotite (ultramafic) bedrock on which this species grows on Mount Tambuyukon and Mount Kinabalu (from ‘peridotite’ the ultramafic bedrock, and; cola (Latin)—to dwell or inhabit). Peridotite is a dense, coarse-grained igneous rock, consisting of olivine and pyroxene minerals (magnesium-iron-silicates). This rock-type, to varying degrees serpentinised, is the main bedrock of ultramafic outcrops in Sabah, and forms the Mount Tambuyukon massif.

Distribution and habitat
Pittosporum peridoticola is found exclusively in ligneous scrub on extreme ultramafic soil on Mount Tambuyukon and Mount Kinabalu. The sites where it occurs are located at 1700–2500 m asl in dense vegetation consisting of shrubs (1–2 m tall). Co-occurring species include: Styphelia malayanus Jack subsp. malayanus (Ericaceae), Phyllocladus hypophyllus Hook. f. (Phyllocladaceae), Weinmannia clemensiae Steenis (Cunoniaceae), Leptospermum javanicum Blume (Myrtaceae), Wikstroemia indica (L.) C.A.Mey. (Thymelaeaceae), Lithocarpus rigidus Soepadmo (Fagaceae), Podocarpus brevifolius (Stapf) Foxw. and Dacrydium gibbsiae Stapf (Podocarpaceae). On the summit ridge of Mount Tambuyukon, Pittosporum peridoticola was found in an area of just a few hundred m2 and only a small number of individuals were seen. Similarly, the habitat on Mount Kinabalu (Mentaki Ridge) is very small, comprising of only a few individuals. Other rare regional species are also known only from populations on ultramafic soils in Kinabalu Park, for example Drosera ultramafica A.Fleischm., A.S.Rob. and S.McPherson (Droseraceae), Nepenthes rajah Hook.f. (Nepenthaceae), Calanthe otuhanica C.L.Chan and T.J.Barkman (Orchidaceae) and Weinmannia clemensiae Steenis (Cunoniaceae).

 John B. Sugau and Antony van der Ent. 2016. Pittosporum peridoticola (Pittosporaceae), A New Ultramafic Obligate Species restricted to Kinabalu Park (Sabah, Malaysia). Botanical Studies. DOI:  10.1186/s40529-016-0119-9