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 x 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 km 2 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 km 2 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. affinis, 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).