Drosera ultramafica ( Droseraceae ) , a new sundew species of the ultramafic flora of the Malesian highlands

Drosera ultramafica, a new montane sundew species endemic to ultramafic soils of the Malesian highlands, is described and illustrated.


INTRODUCTION
Ultramafic soils are highly infertile substrates with unusual rock chemistry (Proctor & Woodell 1975, Proctor 2003).Such soils are commonly referred to as 'serpentine' by plant ecologists, however this term defines a group of minerals, whereas 'ultramafic' or 'ultrabasic' is preferred for rocks, their derived soils and endemic flora (Gibson et al. 1992).These soils are generally poor in plant macronutrients such as nitrogen, phosphorous, potassium and calcium, but also toxic to most plant life due to their high concentrations of nickel, cobalt, chromium and magnesium (Proctor & Woodell 1975, Gibson et al. 1992).Even so, many plants are adapted to ultramafic soil conditions, resulting in a specialized ultramafic flora that often contrasts sharply with the surrounding vegetation in terms of species composition and general appearance, often being rich in endemic taxa (Proctor & Woodell 1975, Brooks 1987).
Ultramafic outcrops are widespread in Malesia (see Map 1), including large areas of Sulawesi, New Guinea and the Philippines (Brooks 1987, Proctor 2003).The low soil nutrient content of ultramafics leads to a rather open vegetation (Nagy & Proctor 1997), providing conditions ideally suited to carnivorous plants, which are adapted to survive on poor soils through the capture of invertebrate prey for additional nutrition.Indeed, a high α-diversity of Nepenthes L. (Nepenthaceae) is confined to ultramafic soils in Malesia (Robinson et al. 2009).
A single, widespread species of Drosera L., Drosera spatulata Labill.has been reported to occur occasionally on ultramafics in Malesia (Van Steenis 1953, Beaman et al. 2001).However, a closer examination of the D. spatulata aggregate by the first author of this study revealed that the ultramafic plants do not represent D. spatulata s.l., but a distinct species that has not been described thus far.
In his treatment of Droseraceae for Flora Malesiana, Van Steenis notes under D. spatulata: "The Sumatran and Philippine specimens [referring to D. spatulata s.str.sensu Labill., collected on the Philippine islands of Luzon and Mindoro] differ slightly from those of Mt Kinabalu [D.ultramafica] by obovate, not acute, petals with slight crenulations towards the apex, by broader bracts, and by a scarcely capitate-glandular inflorescence.The style-arms are sometimes halfway forked for a second time."(Van Steenis 1953).Moreover, this new, stem-forming Drosera had already been reported and pictured from Marai Parai several times under the name D. spatulata (e.g.Diels 1906, Van Steenis 1953, Beaman et al. 2001, Anfraix 2005), as well as from Leuser National Park of northern Sumatra (De Wilde & Duyfjes 2001).A recent expedition to the Philippines (see Robinson et al. 2009, McPherson 2009) has revealed the presence of this new taxon from ultramafic habitats on two different mountains located on the island of Palawan.It is described here from herbarium specimens and observations made during that expedition.

MATERIAL AND METHODS
Herbarium specimens were studied for morphological measurements and taxonomical comparison (A.F.) and notes on habitat and ecology were recorded from the field in Palawan (A.S.R.).Etymology.The epithet denotes the fact that this species is confined to ultramafic soil.
Distribution -Malesia: Philippines, Palawan, Mt Mantalingahan and Mt Victoria; Malaysia, Borneo, Sabah, Mt Kinabalu; Indonesia: Sumatra, Northern Sumatra, Aceh, Gunung Bandahara and Pucuk Angasan; Sulawesi, Central Sulawesi, Buyu Katapasa.Drosera ultramafica is recorded from a number of high elevation (1500 -3000 m) sites in Malesia thus far, and it is likely to be more widespread on suitable mountain ranges in the Malesian Archipelago.Drosera ultramafica has been observed and pictured growing at the summit of Buyu Katapasa in northern Central Sulawesi at 2700 m (U.Zimmermann, pers.obs.), but no herbarium specimens are yet available for Sulawesi (Map 1).
Sparsely scattered populations in Palawan at 1600 -1700 m altitude in seepages on sharply-draining rocky soil.On Mt Mantalingahan, found growing in granular ultramafic soil on open seepages in full sun and among grasses.On Mt Victoria, found primarily among grasses and ultramafic protrusions in well-drained soils thoroughly wetted by regular downpours.Flowers and fruits observed July -August.Plants generally shaded, but exposed to intense midday sunlight and cooled by heavy cloud thereafter.June temperatures to 30 °C during the day, 16 °C at night (pers.obs.).On Mt Victoria, associated species consist predominantly of a Pleomele sp.Notes -Plants of D. ultramafica from Palawan and Central Sulawesi have white petals, whereas plants from Northern Sumatra are pink-flowered.Specimens from Mt Kinabalu, Borneo, are reported to have both pink and white flowers.
Interestingly, seedlings of D. ultramafica bear conspicuous short-stalked glands on their cotyledons.Glandular cotyledons are occasionally found in Drosera species of section Drosera (Conran et al. 1997).
In the Malesian area, D. ultramafica is unlikely to be confused with any other Drosera species except D. spatulata (for differences see Table 1).In the field, sterile plants of D. ultramafica can be distinguished from D. spatulata on sight by their stemforming habit and by the erect to semi-erect narrowly oblong to oblanceolate leaves, which give the overall plant a subglobose appearance (Fig. 1).In contrast, the spathulate to cuneate leaves of D. spatulata are appressed to the ground, forming a    flat rosette.Occasionally, old specimens of D. spatulata may form tall columns consisting of dried leaves (e.g.observed on Mindoro, Fig. 2), but even in these individuals, the leaves are never held erect to semi-erect as in D. ultramafica.The colour of the stipules of living plants is another useful character to tell both species apart: the membranous stipules of D. ultramafica are usually deep red in colour when alive, whereas the stipules of all varieties of D. spatulata are papery white or translucent in living plants.Unfortunately, stipules of both species turn brownish when dried, so this character is not applicable to herbarium specimens.
Drosera spatulata can be found growing in a wide range of nutrient-poor soils in Malesia, ranging from clay-based, mafic laterites, organic soils and peat to pure wet silica sand (Van Steenis 1953, Fleischmann & Lee 2009), but it is apparently always absent in suitable habitats on ultramafic soils.Drosera spatulata is a lowland to submontane species occurring from 10-1400 m altitude (Van Steenis 1953, Conn 1980), but reaching up to 2400 m on Mt Halcon, Mindoro, Philippines (Merrill 1907, pers. obs.).In Sarawak, Borneo, in New Guinea and in eastern Australia, D. spatulata is a species of low altitude savannah and open, usually swampy, heath vegetation (Van Steenis 1947, 1972, Conn 1980, Lowrie 1998, Fleischmann & Lee 2009).Drosera ultramafica is restricted to montane habitats (1500 -3000 m).Due to their different ecological preferences, the species have not been reported as growing sympatrically, and they are unlikely to co-occur naturally.For the same reason, no natural hybrids involving D. ultramafica as a parent are known.
Two species of Drosera from Indochina and New Caledonia respectively are superficially reminiscent of D. ultramafica, but are not recorded from the Malesian area; these can be distinguished from the latter as follows: D. ultramafica differs from the Chinese D. oblanceolata Y.Z.Ruan, which has similar leaves and stipules, in having a glandular-hairy scape, sepals only occasionally reflexed in fruit (usually all five sepals of the calyx with reflexed tips in fruit, as in D. spatulata) and flowers with style arms widened to the tip and a stigmatic tip that is lanceolate to spathulate or bifid (filiform style arms, stigmatic tip bifid or ramifid).In addition, D. oblanceolata is endemic to Hong-Kong (Ruan 1981) and not expected to occur in the Malesian floristic area.
Drosera neocaledonica Raym.-Hamet, an endemic of New Caledonia, shares a similar stem-forming habit and narrowly oblan-ceolate leaves, but differs from D. ultramafica in having bristly white hairs on its petioles, in having a scape and sepals that are covered densely with short-stalked red glandular trichomes, and in the larger flowers (up to 2 cm diam) and styles with stigmatic tips that are branched multiple times.
Drosera neocaledonica is the only other species in the genus other than D. ultramafica that is not only tolerant of ultramafic substrates, but seemingly ecologically restricted to them (Gibson 2001).However, both taxa can be artificially cultivated in peat-based substrates devoid of high concentrations of heavy minerals (Gibson 2001, A. Fleischmann pers. obs.), suggesting that they are not edaphically confined to the soil chemistries of ultramafic regions.Most plant taxa endemic to ultramafites will grow well artificially on non-ultramafic soils in the absence of competition by vigorous plants or phytopathogenic fungi, thus ultramafic soils effectively provide a refuge from biotic factors present in non-ultramafic substrates (Brooks 1987).One other species of Drosera is known to at least tolerate ultramafic substrates: D. arcturi Hook.can occasionally be found growing in wet soil overlying ultramafic rocks in Tasmania (Gibson et al. 1992), but is not generally restricted to such sites, growing well in various types of non-ultramafic peaty soil (Lowrie 1998).