Similar to Goniothalamus tortilipetalus M.R.Hend., but differing from that species in having 308–336 stamens (vs. ca. 170–260) and ca.120 carpels (vs. ca. 50–100) per flower, and stigmas and pseudostyles ca.8.5 mm (vs. 4–4.5 mm) long.

Vietnam, Khanh Hoa Province, Hon Ba Nature Reserve, in evergreen forest near stream, 12°06.51'N, 108°59.23'E, alt. 400 m, Tagane S., Kanemitsu H., Dang V.S., Tran H. with Hanh N., Loi X.N., Thach N.D., Dinh N., Hieu P.N.H. V1497, 12 July 2014, Fl., holotype: KYO!; isotypes: BKF!, FU!, K!, VNM!, the herbarium of Hon Ba Nature Reserve!).

Small trees, 11 m tall, DBH 8 cm. Young twigs sparsely covered with brown hairs, soon glabrous, blackish when dry. Petioles 1–1.2(–1.5) cm long, 2.5–3.5 mm in diam., glabrous, black when dry. Leaf blades narrowly oblong-elliptic, 31–45 × 8.2–11.5 cm, length/width ratio 2.7–4.0, 185–225 µm thick, base acute to obtuse, margin entire, revolute when dry, apex acuminate, acumen ca. 1.5 cm long, leathery, slightly shiny above, glabrous on both surfaces; midribs impressed above, prominent below, glabrous on both surfaces, secondary veins 16–20 pairs, arising at an angle of 60–70 degrees from a midrib, prominent on both surface when dry, glabrous on both surfaces, tertiary veins distinct above, slightly distinct below. Flowers solitary, arising from main trunks and older branches, pendent; pedicels 19–25 mm long, 1.5–2.5 mm in diam., glabrous; bracts 3–4, very broadly triangular to hemiorbicular, ca. 1.6 mm long, brownish pubescent outside, glabrous inside, margin sometimes ciliate. Sepals ovate-triangular, 2.2–2.8 × 2.2–2.8 cm in flower, accrescent, increasing to 3.3 × 3.8 cm in fruit, 200–210 µm thick, basally connate, greenish in vivo, glabrous outside, sparsely covered with brown hairs inside, veins reticulated, distinct outside, indistinct inside. Outer petals oblong-ovate to narrowly ovate, 6–9. 2 × 2.2–3.1 cm, length/width ratio 2.7–3.4, 380–450 µm thick, greenish, glabrescent outside, sparsely covered with short brown hairs inside, except at base velutinous, veins faintly visible outside, indistinct inside. Inner petals rhombic, 1.6 × 0.7 cm, length/width ratio ca. 1.9, 1100–2100 µm thick, greenish, pubescent outside, velutinous inside with 12–14 basal grooves. Stamens 308–336 per flower, flattened-oblong, 3.8–4.8 × 0.6 mm, glabrous; connectives long-apiculate, 1.2–1.5 mm long, apiculate length 0.5–0.9 mm long, densely covered with cream-white hairs. Carpels ca. 120 per flower; ovary 1.4–1.7 × ca. 0.3 mm, densely covered with golden-brown hairs; stigmas and pseudostyles flagellate, ca.8.5 mm long, L-shaped curved in the middle, yellowish in vivo, blackish when dry, glabrous, tip awl-shaped. Fruits with persistent calyx, fruiting pedicels 2.7 cm long, 3–4.5 mm in diam. Monocarps 22, ellipsoid, 1.6–1.7 cm long, ca. 1.0 cm in diam., base attenuate, apex apiculate, glabrous, reddish-brown, pericarp ca. 0.5 mm thick when dry; stipes 0.6–1.2 mm long, ca. 2 mm in diam., glabrous. Seeds one per monocarp, 1.5 cm long, 0.8–1.0 cm in diam., yellowish brown, glabrous, seeds with copious surrounding mucilage.

Figure 1. 

Goniothalamus flagellistylus sp. nov. (a) Leafy branch, (b) portion of abaxial leaf surface, (c) flowers on main trunk, (d) vertical section of flowers, (e) apertures between inner petals, (f–g) mature fruit on older blanch, (h) holotype, (i) pedicel and sepals on old branch, (j) adaxial side of inner petal, (k) stamen, (l) carpel. (h–l) From Tagane et al. 1497. Scale bars (i, j) = 1 cm, (k, l) = 1 mm.

Figure 2. 

Line drawing of Goniothalamus flagellistylus sp. nov. (a) leafy twig, (b) flower on main trunk, (c) outer petal (adaxial), (d) inner petals (ad- and abaxial), (e) Stamens, (f) Carpel. Materials from Tagane et al. V1497.

Mature flowers and fruits were collected in July and November, respectively.

This species is known only from Mt. Hon Ba, Khanh Hoa Province, South Vietnam. The small population was found on a slope in broad-leaved evergreen forest, ca. 100 m apart from a rapid river, where Ixonanthes reticulata Jack, Palaquium sp., Gironniera subaequalis Planch., Archidendron chevalieri (Kosterm.) I.C.Nielsen, Barringtonia augusta Kurz, Barringtonia macrostachya (Jack) Kurz, Camellia krempfii (Gagn.) Sealy, Streblus indicus (Bureau) Corner, Xerospermum noronhianum Blume and Pandanus fibrosus Gagnep. are dominated.

Vietnam, Khanh Hoa Province, Hon Ba Nature Reserve, in evergreen forest near stream, 12°06.51'N, 108°59.23'E, alt. 400 m, Toyama H., Tagane S., Dang V.S., Nagamasu H., Naiki A., Tran H., Yang C.J. with Cuong N.Q., Hieu H.N.P. V1972, 22 November 2014, Fr. (FU!, KYO!, NTU!, VNM!, the herbarium of Hon Ba Nature Reserve!).

The specific epithet is in reference to its flexuous styles which is too long to insert straight in the pollination chamber that formed by the inner petals.

Tagane et al. V1497: LC010815 (rbcL), LC010816 (matK).

Goniothalamus flagellistylus is morphologically similar to G. calvicarpus Craib, G. griffithii Hook.f. & Thomson, and G. tortilipetalus, all of which form a monophyletic group (Nakkuntod et al. 2009) and are characterized by relatively large sepals with distinct veins and stamens with long apiculate connectives (Saunders and Chalermglin 2008). Among the three species, G. flagellistylus is most similar to G. tortilipetalus, which is distributed in the Malay Peninsula, in having more than 200 stamens and more than 50 carpels. In fact, The BLAST similarity search based on the matK sequence of G. flagellistylus resulted in homology as high as 734/736 bp with the sequence of G. tortilipetalus (GeneBank accession no. EU715081) in the DNA database. However, as described in the diagnosis above, the two species can be easily distinguished by the number of stamens and carpels per flower, and style length (Table 1). Also, G. flagellistylus is different from G. tortilipetalus in that flowers arise not only from the main trunk but also from the older branches as in G. calvicarpus and G. griffithii (Saunders and Chalermglin 2008).

Data deficient. Goniothalamus flagellistylus is known from a single population, including only six individuals: only one produces flowers/fruits while the others are just saplings. This situation satisfies the CR (critically endangered) status in criterion D of IUCN Red List Categories (IUCN 2014). However, more individuals could be found if neighboring areas are more thoroughly surveyed. Thus, we regard the conservation status as DD. In Mt. Hon Ba, large areas of primary evergreen forest below 300–400 m elevation had been cleared or selectively logged before the Hon Ba Nature Reserve established, and it is likely that some habitats of this species were lost. The forest habitat where we found G. flagellistylus remains less disturbed under a lower level of logging activities probably because of its landform of the steep slope near the rapid river. The forest in this Nature Reserve is currently protected well from anthropogenic activities, and recovering better and better. The current data available are not enough for a risk evaluation, we therefore need special attention to the individuals/populations of G. flagellistylus and its distribution.