Callmander, M.W. & S. Buerki (2016). Two new threatened species of Benstonea Callm. & Buerki (Pandanaceae) from Sabah (Borneo, Malaysia). Candollea 71: 257–263. In English, English abstract.
Two new species of Benstonea Callm. & Buerki (Pandanaceae) are described from Sabah (Borneo, Malaysia). Benstonea fortuita Callm. & Buerki is only known from a small patch of forest in the southern tip of Crocker Range in the southwest of the state. It is diagnosed by its subacaulescent habit, its leaves abruptly attenuate at the apex and narrowing towards the base, and its solitary globose syncarp on a short peduncle. Benstonea serpentinica Callm. & Buerki is endemic to the ultramafic substrate of Mt. Silam in eastern part of the state ; it is diagnosed by its lateral plurisyncarpic infructescence, its peduncle covered with prophylls at base, and its stout acuminate style. Discussions on the morphological and molecular phylogenetic affinities of the new species are provided. Finally, both new species are assessed as “Critically Endangered” following IUCN Red List Categories and Criteria.
Introduction
Benstonea Callm. & Buerki (Pandanaceae) has been segregated from Pandanus Parkinson based on morphological and molecular phylogenetic evidence (Buerki et al., 2012 ; Callmander et al., 2012). This screw-pine genus includes all species with stigmatic grooves consistently placed on the abaxial side of the style (vs. always adaxial in Pandanus) (Callmander et al., 2012, 2013). Benstonea includes 60 species (incl. the two new species described here) spanning from India to Fiji with centres of diversity in Borneo, Peninsular Malaysia and New Guinea (see Buerki et al., 2016 and references therein).
Borneo (the third largest island of the world and a biodiversity hotspot) hosts the highest species diversity of Benstonea with currently 22 accepted species (82% endemic) representing 37 % of the generic diversity (Callmander et al., 2012). Several other plant families unveil high level of endemism in Borneo, i.e. Arecaeae (see Dransfield et al., 2008; Baker & Couvreur, 2012). The unique floristic diversity of Borneo can be mainly explained by its stable climate sustaining tropical humid forests (Slik et al., 2011) and complex geological history (Hall, 2009). A recent biogeographical study on Benstonea demonstrated that the Bornean species community resulted from multiple independent dispersals from other parts of the Sunda shelf (especially Peninsular Malaysia) taking place from the Miocene onwards (see Fig. 3–4 in Buerki et al., 2016). In most cases, dispersal events seem to have been associated with increases of diversification rates, especially in clade IIIc (Buerki et al., 2016). The biogeographical analysis inferred an origin of this latter clade in Borneo, which was followed by an apparent increase of diversification rate giving birth to 13 species (including the new species B. serpentinica Callm. & Buerki described here) occurring in most ecosystems available on the island. In addition, some of the species of clade IIIc subsequently expanded their range across the Sunda shelf and even the Philippines (e.g. B. affinis (Kurz) Callm. & Buerki) (Buerki et al., 2016).
The authors accompanied by Chris Davidson, Sharon Christoph and a team from SAN conducted fieldwork in Sabah in 2012 and 2014. We targeted areas of high species endemism: Crocker Range, Mt Kinabalu and two ultramafic outcrops (Mt Silam and Mt Tawai) (Wong, 1998 ; van Welzen, 2005 ; Raes et al., 2009 ; van der Ent et al., 2014). These field missions have led to the publication of a new species of Trigonachras Radik. (Sapindaceae) endemic to Mt. Tawai (Buerki et al., 2013) and the discovery of two new species of Benstonea described below. Benstonea fortuita Callm. & Buerki is only known from a small patch of forest in the southern tip of Crocker Range (southwestern Sabah), whereas B. serpentinica is currently restricted to Mt Silam (eastern Sabah) (Fig. 1). Discussions on the morphological and molecular phylogenetic affinities of the new species are provided below along with their preliminary IUCN Red List assessments (IUCN, 2012).
New species
Benstonea fortuita Callm. & Buerki, spec, nova (Fig. 2).
Typus: Malaysia [Borneo]. State Sabah: Tenom Dist., 21 km from Tenom on road to Sipittang, Lumako FR, 5°00′22″N 115°51′53″E, 620 m, 9.X.2014, fr., Callmander et al 1197(holo-: G [G00341180]!; iso-: BM!, SING!, SAN!)
Benstonea fortuita Callm. & Buerki is distinguished among the genus by its subacaulescent habit, its leaf abruptly attenuate at the apex with a short apicule (0.5–1 cm), its ventral pleats armed, its stout acuminate style (3–4 mm), slightly curved proximally, and its solitary globose syncarp.
Subacaulescent shrub < lm tall. Leaves glaucous, white below, 100–120 cm long, 4–5 cm wide in the middle, 3.5 cm wide near the sheath, abruptly attenuate in the upper part, shortly apiculate (c. 0.5–1 cm long), narrowing towards the base, subcoriaceous; marginal prickles beginning at 6–9 cm above the base and extending to the apex, antrorse, c. 2 mm in the lower third, 2–6 mm apart, to c. 1 mm in the mid third, 5–10 mm apart; minute in the distal third, c. 2 mm apart; ventral pleats armed in the last 25–28 cm of the leaf with minute prickles; sheath not auriculate, whitish. Infructescence terminal, monosyncarpic, erect at maturity; syncarp in the middle of the clump of leaves, pale green, subglobose, c. 6 cm in diam.; peduncle straight, 10 cm long, 0.7 cm wide at apex, trigonous, white in vivo, longitudinal veins visible, covered with 4–5 bracts scars. Drupes c. 150, 23– 25 mm high, 4–6 mm wide, c. 6 mm in depth, 5–6-angled; pileus pyramidal, pale to dark green in vivo, shrunk when dried, 8–10 mm high (excluding style). Style unique, stout acuminate, 3–4 mm long, slightly curved proximally; stigmatic groove brown in vivo, linear, positioned on abaxial side; endocarp c. 6 mm long, walls c. 0.4 mm thick; seed locule elliptic, 4 × 3 mm; apical mesocarp fibrous, discrete, c. 4 mm long; lower mesocarp fibrous. Staminate plant unknown.
Etymology. — This species is only known from a single population where only one fruiting individual was observed. We were very fortunate to come across this rare and discrete taxon and the species epithet reflects our feeling when we discovered this new Benstonea.
Distribution and ecology. — Benstonea fortuita is only known by few individuals in southwestern Sabah in the lowland Dipterocarp forest at an altitude of 600 m (Fig. 1).
Conservation status. — Despite being known from a Forest Reserve [FR], this species is considered rare and seriously threatened. The only known population is located in the southern tip of the Lumako FR in a secondary Dipterocarp forest where few dominant trees still protect the understorey due to past logging. Benstonea fortuita is assigned a preliminary status of “Critically Endangered” [CR Blab(i,iii,iv,v)] following IUCN Red List Categories and Criteria (IUCN, 2012).
Notes. — The overall morphology of the new species can be compared to: B. glaucophylla (Ridl.) Callm. & Buerki, B. parva (Ridl.) Callm. & Buerki, and B. undulifolia (Ridl.) Callm. & Buerki. All three species share wide, abruptly attenuate leaves and a solitary syncarp with B. fortuita. Nevertheless, the new species can easily be discriminated from these species by the combination of characters presented in Table 1.
In their phylogeny, Buerki et al. (2016) showed that the new species B. fortuita belongs to clade I together with the endemic Bornean B. platystigma (Martelli) Callm. & Buerki. Although both species have the same ecology (lowland humid forest), B. fortuita can easily be distinguished from B. platystigma by its habit (subacaulescent shrub <1 m tall vs. low shrub), leaves (wide, 4.5 cm and apex abruptly attenuate vs. narrow, 1.5 cm and apex gradually attenuate), style and stigmatic groove (stout acuminate, slightly curved proximally with a linear stigmatic groove vs. antrorsely bent down, flattened proximally with a subreniform groove) and fruits (pale green syncarp when ripe vs. bright red syncarp when ripe).
Fig. 1.
Distribution of Benstonea fortuita Callm. & Buerki (white star) and B. serpentinica Callm. & Buerki (white circle) in Borneo.
Abbreviations: 1. Crocker Range National Park; 2. Kinabalu Park.
Benstonea serpentinica Callm. & Buerki, spec, nova (Fig. 3).
Typus: Malaysia [Borneo]. State Sabah: Lahad Datu Distr., Gunung Silam, 4°58′14″N 118°10′44″E, 365 m, 3.X.2014, Callmander, Buerki & Jumian 1187 (holo-: G [G00341664]!; iso-: BM!, MO!, SING!, SAN!).
Benstonea serpentinica Callm. & Buerki is distinguished among the genus by its lateral infructescence, its peduncle covered with prophylls at base, its pileus peeling at maturity, its short stout style (2–3 mm), and the pale green fruit colour of its syncarp when ripe.
Treelet to 5–8 m tall, 10 cm dbh, with wide cones of proproots at the base. Each clump of leaves with several lateral erect infructescences. Leaves 300–400 cm long, 5–5.5 cm wide in the middle, 6–6.5 cm wide near the sheath, gradually attenuate in the upper part, flagellate (flagellum 22– 25 cm long), coriaceous; prickles white in vivo; marginal prickles beginning at 10–12 cm above the base and extending to the apex, antrorse (rarely retrorse in the lower 1/3), 2.5–3 mm in the lower third, (3-)4-6(-7) mm apart, strong, to c. 2 mm in the mid third; (3-)4-8(-10) mm apart, to <1 mm in the distal third, 3–6 mm apart; midrib armed at 10–15 cm above base, prickles strong in the lower part, c. 5 mm long, getting smaller through the apex, c. < 1 mm long in the apical part; ventral pleats armed at the distal part of the leaf, prickles discrete, c. <1 mm long, irregularly spaced; sheath 8–10 cm long, c. 7 cm wide at apex c. 10–12 cm large at base. Infructescence lateral, with 7–9 syncarps pending at maturity; syncarp 5-7 × 6-8 cm, ovoid, compressed dorso-ventrally, the distal syncarps globose and smaller (not compressed); peduncle curved (rarely straight), 20–25 cm long, 1.3–1.5 cm wide at apex, slightly flattened, veins and bracts scars visible, covered with several prophylls at base; the latter 2-4 × 14-20(-26) cm long, coriaceous, attached at the base of the peduncule. Drupes >300 per syncarp, 15–20 mm high, 4–5 mm wide, 2–4 mm in depth, 5-angled; pileus pyramidal, pale green in vivo, 3 mm high (excluding style), covered with a white waxy surface, remaining attached and peeling at maturity, revealing the connate part of the drupes. Style unique, brown in vivo, stout, straight, shortly acuminate, slightly curved at apex, 2–3 mm long; stigmatic groove linear, positioned on abaxial side; endocarp c. 5 mm long, walls c. 0.2 mm thick; seed locule elliptic, 2-3 × 3-3.5 mm; apical mesocarp chamber large, ovoid, c. 5.5 mm long; lower mesocarp fibrous. Staminate plant unknown.
Etymology. — The species epithet refers to the ultramafic rocks of Mt. Silam where the species was collected and is confined. Serpentine outcrops cover c. 3,500 km2 across the Sabah state (Proctor et al., 1988). These patches of ultrabasic rock are home to several endemic species (see van der Ent, 2014 for more details on the plant taxa and their distributions).
Distribution and ecology. — Benstonea serpentinica is endemic from Mt. Silam on ultramafic soil in the eastern region of Sabah (Fig. 1). This mountain, which culminates at 884 m, is home to several endemic species including the recently described Ardisia silamensis Utteridge, Julius & Suzana (Utteridge et al., 2014).
Conservation status. — Populations of Benstonea serpentinica are only known from 350 to 600 m on Mt. Silam. This patch of forest on ultramafic substrate represents c. 10 km2 and is part of the Sapagaya FR. Logged forest, palm oil plantations and roads surround nevertheless this mountain, which is under serious human pressure. The new species is therefore preliminary assessed here as “Critically Endangered” [CR B1ab(iii)] following IUCN Red List Categories and Criteria (IUCN, 2012).
Notes. — Benstonea serpentinica is most similar to B. affinis, but differs by its peduncle (short, 20–25 cm, covered with several prophylls at base vs. long, 40–45 cm, with no prophylls), its smaller drupes (15-20 × 4-5 mm vs. 30 × 8 mm) and style (2–3 vs. 7 mm), style morphology (stout, shortly acuminate, slightly curved proximally vs. spiniform, curved proximally) and fruit colour when ripe (pale green vs. red).
In their phylogeny of Benstonea, Buerki et al. (2016) showed that the new species B. serpentinica belongs to clade IIIc together with B. affnis, which is widespread across the Sunda shelf (including the Philippines).
Paratypus. — Malaysia [Borneo]. State Sabah: Lahad Datu Distr., Gunung Silam, 4°58′01″N 118°10′28″E, 620 m, 1.X.2014, Buerki et al. 342 (BM, G, PH, SAN).
Fig. 2.
Benstonea fortuita Callm. & Buerki. A. Habit; B. Infructescence; C. Close up of styles and stigmas.
[Callmander et al. 1197] [Photos: M. Callmander]
Table 1.
Key morphological differences between Benstonea fortuita Callm & Buerki, B. glaucophylla (Ridl.) Callm. & Buerki, B. parva (Ridl.) Callm. & Buerki, and B. undulifolia (Ridl.) Callm. & Buerki.
Acknowledgements
We are very grateful to Chris Davidson, Sharon Christoph, Postar Miun and Jeisin Jumian for the great fieldwork in Sabah in 2014. We would like to thank Abdul Fatah Amir (Sabah Biodiversity Centre) for facilitating the collecting permits in Sabah; Datuk Sam Mannan (Sabah Forestry Department), Lee Ying Fah (Forest Research Center), John B. Sugau and Joan Pereira (SAN) for their support during our research in Sabah. Finally we thank the Idaho Botanical Research Foundation for generous support for fieldwork, Matthieu Berthod for preparing the map, and Fred Stauffer for his careful review of the manuscript.
