Wrightia nuichuaensis Tagane & V.S.Dang, 2025

Tagane, Shuichiro, Dang, Van-Son, Truong, Ba Vuong, Nguyen, Quoc Bao, Pham, Quoc Trong, Nguyen, Tran Vy, Yamamoto, Takenori, Kongxaisavath, Deuanta & Souladeth, Phetlasy, 2025, Wrightia nuichuaensis (Apocynaceae), a new species from southern Vietnam, Phytotaxa 683 (1), pp. 87-90 : 87-89

Wrightia nuichuaensis Tagane & V.S.Dang , sp. nov. ( Fig. 1 )

TYPE: — VIETNAM. Ninh Thuan Province. Nui Chua National Park , 11.78252°N, 109.18305°E, 39 m elev., 22 Dec 2023, fl., S. Tagane et al. N358 ( holotype VNM00070330 !; isotypes FOF0009029 !, KAG186357 !, KYO) .

The new species is characterized by its shrubby habit up to 3 m tall, glabrous plant body except ciliolate calyx lobes and papillose corolla, 4–7 pairs of secondary veins, orange-reddish corolla, stamens inserted at 0.6–0.7 of corolla tube length from the base and only upper part ( 0.6–0.9 mm long, 1/3–1/4 of the total length) of anthers exserted from tube, and simple antepetalous corona lobes shorter than 1 mm, by which combination it is clearly distinguished from the previously known species in the genus.

Shrub, up to 3 m tall, with white latex. Young twigs yellowish brown to reddish brown, glabrous, old branches dark grayish brown with pale round lenticels. Leaves opposite; blades elliptic, elliptic-oblong, or elliptic-obovate, 4.3–10.8 × 2.1– 5.5 cm, dark yellow-green adaxially, dull brownish yellow abaxially, glabrous on both surfaces, apex acuminate, acumen ca. 0.9 cm long, margin entire, recurved, base cuneate, midrib sunken adaxially, prominent abaxially, secondary veins 4–7 pairs, sunken adaxially, prominent abaxially, tertiary veins reticulate, visible adaxially; petioles 3–7 mm long, glabrous, sunken adaxially, rounded abaxially. Inflorescence cymose, terminal, 3–13-flowered, up to 2.7 cm long, peduncle 2.2–4 mm long, glabrous; bracts ovate-triangular, 0.9–2.2 mm long, glabrous on both surfaces. Flowers pendulous; pedicels 4–5 mm long (at anthesis), glabrous. Calyx lobes 5, green, ovate-triangular, 1.7–2.0 × ca. 1.2 mm, apex obtuse, margin ciliolate, colleters in the sinuses inside, obovate-oblong, 0.7–0.8 × 0.3 mm, apex rounded, sometimes with an additional side lobe. Corolla rotate, orange-red, aestivation sinistrorse; tube ca. 2.8 mm long, widening at 1 mm, glabrous inside, densely papillose outside; lobes spreading, broadly ovate to ovate-elliptic, 8.0 × 6.1 mm, reflexed when fully opened, margin of apical part recurved, densely papillose on both surfaces, apex acute to rounded, ciliolate. Corona of one whorl, antepetalous, simple; antepetalous corona basally adnate to corolla for ca. 3 mm long, lobes shorter than 1 mm, margin shallowly irregularly undulate. Stamens 5, attached in a ring to the style head, inserted at 0.6–0.7 of corolla tube length from base; filaments ca. 0.8 mm long, flattened, anthers narrowly triangular, ca. 2.7 mm long, glabrous, base sagittate. Gynoecium of two apocarpous ovaries united into a common style; ovary ovoid-ellipsoid, ca. 1.2 mm in diam., ca. 0.8 mm in diam., glabrous; style and style head ca. 0.7 mm long. Fruits and seeds not seen.

Distribution:— Vietnam (so far known only from the type locality).

Habitat:— Evergreen broad-leaved forest; on gray-brown soil, medium- to coarse-grained granite (not limestone area); 39 m elev.

Etymology:— Species epithet refers to the type locality of the new species.

Phenology:— Flowering in December.

Vernacular name:— Lòng mức Núi Chúa (Vietnamese).

Conservation status:— Data deficient (DD). Currently, Wrightia nuichuaensis is known only from a single location in the Nui Chua National Park. In our field excursion, we found one small population with fewer than 20 mature individuals, which satisfies the criteria of D of Critically Endangered (CR). However, considering the total land area of the national park is about 225 km ² and large parts are covered with thick, evergreen broad-leaved forests, more populations could exist in the park and surrounding areas.

Notes:— Among nine species of Wrightia previously known from Vietnam ( Middleton 2014, Hazell et al. 2023), W. nuichuanensis may resemble W. annamensis Eberhardt & Dubard (1913: 38) in having reddish corolla and upper part of anthers exserted from corolla tube. However, it is distinguished by its fewer secondary veins (4–7 pairs in W. nuichuaensis vs. 10–16 pairs in W. annamensis ), smaller corolla lobes (8 × 6 mm vs. 10.5–15 × 4–5.5 mm), simple and shorter corona (corona lobes shorter than 1 mm vs. corona 2 whorls and lobes longer than 3.2 mm long), and apocarpous ovaries (vs. syncarpous).

In the Nui Chua National Park, 1,514 vascular plants belonging to 596 genera and 147 families have been recorded to date ( Nui Chua National Park 2024). Among them, several species were described in recent years after 2000 based on the specimens collected from the national park, such as Licuala longiflora Henderson et al. (2008a: 150) , Calamus nuichuaensis Henderson et al. (2008b: 196) , Pinanga nuichuensis Henderson et al. (2010: 38) , Aristolochia nuichuaensis T.V.Do & Luu in Do et al. (2019: 108), Balanites vietnamica Luu, T.T. Nguyen & T.Q.T.Nguyen in Nguyen et al. (2023: 57), Lasianthus nuichuaensis V.S. Dang & Naiki (2023: 108) , and Memecylon longipedunculatum Tagane, V.S.Dang & Nuraliev in Tagane et al. (2025), indicating further efforts to write floristic inventories and subsequent taxonomic studies will be needed to accurately understand the overall flora of the area.

Figures

FIGURE 1. Wrightia nuichuaensis. A & B. Flowering branches. C. Twig. D. Abaxial leaf surface. E. Inflorescence, side view. F. flower buds. G. Flowers. H. corolla, back view. I. longitudinally dissected flower. J. pedicel, calyx and pistil (two calyx lobes removed). Photos of Tagane et al. N358 when it was alive, taken by S. Tagane (A–G) and B.V. Truong (H–J).