Nymphanthus adenophorus Tk.Yamam., Tagane & V.S.Dang, 2025

Nymphanthus adenophorus Tk.Yamam., Tagane & V.S.Dang , sp. nov.

Type:— VIETNAM. Ninh Thuan Province: Ninh Hai District, Nui Chua National Park , 11.74647°N, 109.21991°E, 25 m elev., 20 December 2023, S. Tagane, V.S. Dang, P. Souladeth, B.V. Truong, T.V. Nguyen, Q.T. Pham, Q.B. Nguyen, D. Kongxaisavath, T. Yamamoto, K. Yamazaki N226 [fl. & young fr.] ( holotype VNM00072234 !, GoogleMaps isotypes FOF0008897 !, KAG186121 !, KAG186225 !). Figures 1 View FIGURE 1 & 2 View FIGURE 2 . GoogleMaps

Among Nymphanthus species distributed in Vietnam and adjoining countries, N. adenophorus is similar to N. pireyi (endemic to Central Vietnam) and N. nanellus (endemic to South China) in having small leaf blades (≤ 1 × 1 cm) of ovate, suborbicular to obovate shapes, sepals of both staminate and pistillate flowers with non-fimbriate margins, and pistillate flowers bearing connate (not free) discs surrounding the lower portion of the ovary. However, the new species can be clearly distinguished by its terete, shorter ( 1.1–2.3 cm), and fewer-leaved (5–9 leaves) floriferous branchlets (vs. angular, 4–6 cm, and 8–34-leaved in N. pireyi ; 2-winged, 3.8–8 cm, and 22–38-leaved in N. nanellus ), relatively larger leaf blades (6–10 × 6–9 mm vs. 5–7 × 3–4 mm in N. pireyi ; 4–5 × ca. 2 mm in N. nanellus ), faintly visible lateral veins on both surfaces of the leaf blades (vs. slightly conspicuous on the adaxial surface, and inconspicuous on the abaxial surface in both species), longer pedicels of the staminate flowers ( 7–13 mm vs. 1–2 mm in N. pireyi ; ca. 2 mm in N. nanellus ), and pistillate flowers with accordion-folded discs (vs. cupshaped in N. pireyi ; discoid in N. nanellus ) ( Table 1 View TABLE 1 ).

Description:—Prostrate subshrubs up to 50 cm tall, monoecious, all parts glabrous. Branches reddish light green when young, later becoming reddish brown, terete to slightly furrowed (not angular), bearing fascicules of 1–3(–4) floriferous branchlets on each node; floriferous branchlets short and slender, 1.1–2.3 cm long, 0.2–0.5 mm thick, reddish light green, terete (not angular nor winged). Stipules in pairs, narrowly deltate to trullate, 0.3–1.2 × 0.2–0.5 mm, reddish light green to reddish purple, acute to attenuate at apex, margin entire. Leaves alternate, 5–9 per branchlet; petioles 0.4–1.1 mm long; leaf blades broadly obovate to broadly elliptic, sometimes suborbicular, 6–10 × 6–9 mm, chartaceous, grayish red when young, later becoming green, abaxial surface slightly glaucous, rounded to retuse at apex, obtuse to rounded, slightly oblique at base, margin entire, slightly recurved, midveins not prominent on both surfaces, lateral veins 2–3 pairs, faintly visible on both surfaces. Inflorescences axillary, unisexual; staminate inflorescences 1-flowered or fascicle with 2(–3) flowers on proximal to middle axils of branchlets; pistillate inflorescences 1-flowered on distal axils. Bracts ovate, 0.3–0.5 × 0.2–0.3 mm, acute to acuminate at apex, cuneate at base, margin entire. Staminate flowers: pedicels 7–13 mm long, slender, slightly dilated near distal end, pink to purplish red; sepals 4, erect, ovate, 1.3–1.9 × 0.6–1.1 mm, purplish red, obtuse to rounded at apex, margin entire; discs 4, alternisepalous, free, elliptic to cordate, surface foveolate with many glands; stamens 2, glabrous, filaments united throughout their length, forming staminal column 0.8–0.9 × 0.2–0.3 mm, anthers ca. 0.2 × 0.5 mm, thecae 2 per anther, transversely dehiscent; pistillode absent. Pistillate flowers: pedicels 1.3–2 mm long, dilated acropetally, purplish red; sepals 6 in 2 whorls, slightly spreading, elliptic to ovate, 1.5–2.1 × 0.8–1 mm, white to purplish red, obtuse to rounded at apex, margin entire; discs connate (not free), surrounding base of ovary, accordion-folded with 6 antesepalous ridges and 6 alternisepalous valleys, surface foveolate with many glands; ovary superior, 3-locular, depressed globose, ca. 0.6 × 0.9 mm, with 6 longitudinal furrows, surface smooth; styles up to 0.1 mm long; stigmas almost completely bifid to base, 0.4–0.6 mm long; staminodes absent. Capsules (immature) subglobose, 2–3 mm in diam., purplish red, glabrous, smooth. Seeds (immature) trigonous, 2 per locule, light brown, surface smooth.

Distribution: — VIETNAM. Ninh Thuan Province (so far known only from the type locality).

Habitat and ecology: — Nymphanthus adenophorus is prostrate subshrubs in open scrublands on rocky slopes at 25 m elev., which is ca. 150 m away from the coast. The specimen with flowers and young fruits was collected in December.

Etymology: —The specific epithet adenophorus is derived from the presence of many distinct glands on floral discs.

Vernacular name: —Diệp hạ châu núi chúa.

Preliminary conservation assessment:— Data deficient (DD). During six days of our field survey conducted in/around the Nui Chua National Park in 2023, Nymphanthus adenophorus was found only in one locality, at an open coastal scrubland ca. 150 m away from the coast, where we confirmed ca. 50 mature individuals. Although the number of known populations and individuals are very limited, the similar environment is widely seen around the type locality mostly as parts of the Nui Chua National Park, which encloses ca. 33 km of coastline. Additional populations can be found in the coastal area of the national park and its vicinity, and thus further floristic investigations are needed to elucidate the distribution range of this species. Given the inadequacy of the information of its distribution and number of individuals, we here propose Data deficient (DD) according to the IUCN Red List Categories ( IUCN 2024).

Notes:— Nymphanthus adenophorus is distinguished from other Nymphanthus species distributed in Vietnam by the combination of the following features: prostrate subshrubs up to 50 cm tall, floriferous branchlets 1.1–2.3 cm long with 5–9 leaves, leaf blades broadly obovate to broadly elliptic, sometimes suborbicular, 6–10 × 6–9 mm, sepals of staminate and pistillate flowers with non-fimbriate margins, staminate flowers on pedicels 7–13 mm long, and glabrous and smooth capsules.