Orophea chalermprakiat Damth., Chanthamrong & Chaowasku, sp. nov. (Figs 1, 2)

Type:— THAILAND. Satun Prov.: Talu Cave, La-ngu Distr., 21 Nov 2020, fl. & fr., Chaowasku 219 (holotype: CMUB003998801; isotypes: BK, CMUB, PBM, QBG).

The new species is morphologically most like O. sichaikhanii but differs from it by having pilose-villous young twigs and petioles, shorter petioles, rounded to subcordate (rarely obtuse) leaf bases, shorter flowering pedicels, longer inner petal claws, lower number of carpels per flower and longer monocarp stipes (Table 1).

Treelets or trees 3–8 m tall. Young twigs pilose-villous with mostly erect hairs. Petiole 1.5–3.0 mm long, pilose-villous with erect hairs, slightly grooved above; leaf blade elliptic to obovate, 7.6–16.8 × 2.7–6.2 cm, glabrous above, puberulous-pilose (or slightly sparser) with appressed hairs below, base rounded to subcordate, rarely obtuse, apex caudateacuminate (acumen usually 8.0–20.0 mm long); midrib slightly sunken above, glabrous, raised below, pilose with mostly appressed hairs; secondary veins 9–14 per side, prominent below, apical end of adjacent ones often joining into loops, angle with midrib 38°–45° (at middle part of leaf blade); tertiary veins reticulate, sometimes reticulate-percurrent. Inflorescences 2–6-flowered, axillary (sometimes leaf absent); peduncle 3.0–6.0 mm long, almost glabrous; rachis ca. 2.5 mm long when present, almost glabrous, bracts present; pedicel 4.5–6.5 mm long, almost glabrous, bearing 1 triangular bract at ± halfway between pedicel midpoint and sepals. Sepals nearly half-connate, ± broadly ovate-triangular, 1.8–2.1 × 1.8–2.2 mm, outside pilose with appressed hairs, margin villous with erect hairs, inside glabrous. Petals ± cream in vivo at maturity; outer petals broadly ovate to subcircular, 5.5–6.2 × 4.8–5.5 mm, outside almost glabrous, margin tomentose with erect and appressed hairs, inside glabrous; inner petals ± trullate, 10.5–11.7 × 3.6–4.2 mm, connivent at anthesis (but ± apical half of inner petals separate), apex obtuse, claw 3.1–3.6 mm long, outside of inner petals glabrous, margin glabrous only on claw and basal part of blade, remaining area puberulous-tomentose with mostly appressed hairs, inside puberulous-tomentose on bilateral midline on apical half of inner petals, middle part of inner petals (above nectary glands) curly-villous, remaining area glabrous, nectary glands on inside located on basal half of blade, paired short slits. Stamens 9 per flower, 1.0– 1.3 mm long, staminodes absent. Carpels 9 per flower, 1.0– 1.2 mm long; stigmas ± globose; ovaries almost glabrous; ovules 2 per ovary, lateral, uniseriate. Torus slightly elevated, flat-topped, puberulous-pilose with erect hairs. Monocarps up to 9 per fruit, globose, rarely shortly oblongoid, 9.0–12.0 × 9.0– 10.5 mm, smooth (but wrinkled when dry) and glabrous, stipe 8.0–11.0 mm long, glabrous, often attached obliquely to monocarps; fruiting pedicel up to 10.0 mm long. Seed(s) 1–2 per monocarp, ± subglobose (but flattened on one side when there are two seeds in a monocarp), ca. 9.0 × 7.0 mm, smooth (but somewhat wrinkled when dry).

Etymology: —Derived from a Thai royal term meaning “honour”, the specific epithet honours King Rama X of Thailand on the auspicious occasion of his 72 nd (6 th cycle) birthday anniversary (28 July 2024).

Distribution: —Endemic to Satun Province, southern Thailand.

Habitat and phenology: —Evergreen forests in a limestone sink, ca. 25 m. Flowering and fruiting material collected in November.

Additional specimens examined (paratypes): —Same location and date as the type specimens, Chaowasku 220 (CMUB), fl. (young) & fr.; Chaowasku 221 (CMUB), fr.; Chaowasku 222 (CMUB), fl. (young) & fr.; Chaowasku 223 (CMUB), fr.

Notes: —Although not less than 15 mature individuals of O. chalermprakiat have been observed, we believe more exploration on nearby karst areas may uncover additional individuals. Consequently, the category data deficient (DD; IUCN Standards and Petitions Committee 2022) is suitable here.