Tên Khoa học: Goniothalamus flagellistylus Tagane & V. S. Dang
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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.

Distribution and habitat

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.

Conservation status

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.