Saprosma nuichuaensis Q.T.Pham, V.S.Dang & Tagane, sp. nov. (Figures 1, 2)

TYPE:— VIETNAM. Ninh Thuan Province, Ninh Hai District, Nui Chua National Park, in evergreen forests, 11°46'21.50"N, 109°10'09.37"E, at elevation 259 m a.s.l., 22 December 2023, with flowers and fruits, S. Tagane et al. N376 (holotype: VNM [VNM00070333!]; isotypes: FOF [FOF0009047!], KAG [KAG186375!], VNM!).

Diagnosis: — Saprosma nuichuaensis is morphologically similar to S. ternata in having shrubby habit and terminal inflorescence with long peduncle 1–4.5 cm long, but differs in having terete branches (vs. angled in S. ternata), opposite leaves (vs. whorls of 3 or sometimes opposite), smaller leaf blades (5–9.5 × 2–3.5 cm vs. 8–15 × 3–6.5 cm), fewer secondary veins (5–8 pairs vs. 7–10 pairs), shorter petioles (2–5.5 mm long vs 6–12 mm long), smaller calyx lobes (0.2–0.5 mm long vs ca. 1 mm long), and abaxially verrucose seed surface (vs. smooth).

Shrubs, up to 2 m tall. Young branches terete, ca. 2 mm in diam., green in vivo, dull yellowish-brown to reddish brown in sicco, glabrous; internodes (0.7–) 2–6 cm long. Leaves opposite; blades elliptic, oblong-elliptic, oblonglanceolate, 3.9–10.2 × 1.5–4.3 cm, subcoriaceous, dark grayish brown to dark brown adaxially, pale gray to yellowish brown abaxially, glabrous on both surfaces, apex acuminate, base acute to cuneate, margin entire, recurved when dry, midrib prominent to flat adaxially, prominent abaxially, secondary veins 5–8 pairs, ascending at the angle of 40–60° from midrib, curved to the margin, without domatia, tertiary veins reticulate; petioles 2–5.5 mm long, brackish in sicco, glabrous. Stipules narrowly triangular to lanceolate, 2–2.5 mm long, glabrous on both surfaces, caducous. Inflorescences terminal and in the axils of leaves, cymose, 1.5–4.5 cm long, 1–5-flowered; peduncles 0.6–1.5 cm long; bracts triangular-lanceolate, 1–4 mm long, puberulent on both surfaces. Flowers 4-merous, sessile to short pedicellate in anthesis, elongated to 4 mm long in fruiting; calyx obconical to campanulate, tube 1–2 mm long, yellowish green in vivo, blackish in sicco, glabrous, lobes 4, very broadly triangular, 0.2–0.5 mm long, glabrous, apex acute; corolla cylindrical, white, tube 3–7 mm long, outside puberulent on upper part, inside villous, lobes 4, triangular with expanded crisped margins, 2–3 mm long, pubescent on both surfaces, apex acuminate, the throat hairy; stamens 4, partially exserted, filaments ca. 1 mm long, basally connate to corolla, anthers ca. 0.5 mm long, dorsifixed near base; ovary 2-locular, ovules 1 in each locule, style 1–1.2 mm long, stigma 2-lobed, included or exserted. Fruits subglobose to obovoid-ellipsoid, 7–10 mm long, ca. 6 mm in diam., green when young, dark blue-purple when ripe, glabrous; pyrenes 2. Seeds plano-convex, 5–7 mm long, verrucose abaxially, endosperm fleshy, blackish brown when dry.

Additional specimens examined (paratype): — VIETNAM. Ninh Thuan Province, Ninh Hai District, Nui Chua National Park, in evergreen forests, 11°44’06.14”N, 109°13’05.20”E, 212 m elevation, 20 December 2023, with flowers and fruits, S. Tagane et al. N190 (FOF [FOF0008858!], KAG [KAG186189!], VNM!).

Distribution, habitat and phenology: — Vietnam (so far known only from Nui Chua National Park, Ninh Thuan Province). Saprosma nuichuaensis was found in an evergreen forest at 100–300 m elevation. Flowering and fruiting in December.

Etymology: —The species epithet is named after its type locality, Nui Chua National Park, Ninh Thuan Province, Vietnam.

Vernacular name: —Hoại hƯƠng núi chúa.

Preliminary conservation status: —Endangered (EN). Saprosma nuichuaensis is only known from two populations in Nui Chua National Park, Ninh Thuan Province, Vietnam. The Extent of Occurrence (EOO) is less than 298 km 2, corresponding to the area of the national park and the known Area of Occupancy (AOO) is 8 km 2. In each population, about 60 mature individuals were observed along nature trails in an evergreen forest. Considering the forest along nature trails is easily affected by human tourism activities, we propose the category of S. nuichaensis as Endangered (EN) according to the IUCN Red List Categories and Criteria, B1a, b(i, ii, iii) + B2a,b(i, ii, iii) + D (IUCN 2024).

Notes:— This new species resembles Saprosma ternata, which is known from Bangladesh, Bhutan, China, India, Laos, Malaysia (Peninsula), Myanmar, Thailand, and Vietnam, but differs from that species based on several morphological characteristics summarized in Table 1. In addition to S. ternata, S. nuichuaensis may resemble S. annamensis in its leaf shape and size, but is distinguished by its longer petioles 2–5.5 mm long (vs. to 2 mm long in S. annamensis), 4-merous flowers (vs. 5-merous), and longer corolla tube 3–7 mm long (vs. 2.5 mm long) (Table 1).

According to the classifications of Rydin et al. (2009), Saprosma nuichuaensis is placed in the tribe Paederieae de Candolle (1830: 342) subfamily Rubioideae Verdcourt (1958: 280), together with four genera, Leptodermis Wallich (1824: 191), Paederia Linneaus (1767: 189), Serissa Commerson ex Jussieu (1789: 209), and Spermadictyon Roxburgh (1815: 32), in the point of its small shrubs, often foetid, flowers 4-merous, stamens inserted in the corolla tube, ovary 2-locular with a single erect ovule in each locule, and fruits indehisce when dry.