Lasianthus trongii V.S.Dang, T.A.Le & Tagane, 2025

Dang, Van-Son, Le, Tuan Anh, Hoang, Thanh Son, Le, Van Son, Ha, Van Bac, Pham, Quoc Trong, Phetlasy, Souladeth, Tagane, Shuichiro & Naiki, Akiyo, 2025, Two new species and one new addition of Lasianthus (Rubiaceae) for the flora of Vietnam, Phytotaxa 694 (1), pp. 57-67 : 58

Lasianthus trongii V.S.Dang, T.A.Le & Tagane , sp. nov. Figures 1 & 2 .

TYPE:— VIETNAM. Quang Tri Province: Vinh Linh District, Hien Thanh Commune , in secondary forests, 17°03′35.03′′N, 107°04′23.02′′E, 50 m elevation, 19 November 2022, Le Tuan Anh & Van-Son Dang LTA001 (holotype VNM [ VNM00070334 !]; isotypes VNMN!, VNM [ VNM00070775 !]) .

Diagnosis: — Lasianthus trongii is closely related to L. tamdaoensis V.S.Dang in Dang & Naiki (2019: 51) in the shape of the leaves and inflorescence with long peduncle, but it can be distinguished from latter by its branches glabrous (vs. densely appressed pubescent to strigose), petioles 2–3 mm long (vs. 3–5 mm long), calyx 4-lobed (vs. 5-lobed), corolla tube 4–4.5 mm long (vs. 5–6 mm long), lobes 1–1.2 mm long (vs. 2–4 mm long), fruits reddish-orange (vs. blue), and pyrenes 4 (vs. 5).

Shrubs 1–3 m tall; branches ca. 2 mm in diam., glabrous; internodes 2–4 cm long. Leaves opposite; blades lanceolateelliptic or lanceolate, 8–12 × 2–3 cm, subcoriaceous, glabrous on both surfaces, apex caudate-acuminate, 1–1.5 mm long, base subrotund, margin entire, midrib flat adaxially, prominent abaxially, secondary veins 6–8 pairs, ascending at the angle of 40–50° from the midrib, curved to the margin, prominent abaxially, tertiary veins parallel, faint adaxially, prominent abaxially; petioles 2–3 mm long, glabrous. Stipules small, narrowly triangular, 0.8–1 mm long, sparsely strigose at the base only. Inflorescences cymose, up to 7-flowered; peduncles 2–3.5 cm long, sparsely strigose. Bracts persistent, linear to lanceolate, 1–2 mm long, pubescent. Flowers subsessile. Calyx campanulate to obconical, glabrous, tube 1.7–2.5 mm long, pale-green in vivo, lobes 4, triangular, 0.5–1 mm long, sparsely strigose toward apex, apex acute. Corolla cylindrical, tube 4–4.5 mm long, white, puberulent outside on the upper part, lobes 4, oblong-triangular, 1–1.2 mm long, pubescent outside, villous inside. Stamens 4, inserted at corolla tube; filaments 0.7–0.9 mm long, basally connate to corolla; anthers oblong, 0.3–0.5 mm long. Ovary 4-locular; style 1.5–2 mm long, pubescent; stigma 0.3–0.5 mm long, 3-lobed. Drupes ovoid to subglobose, 1.0– 1.2 cm long, ca. 1.0 cm in diam., glabrous, reddish-orange when ripe; pyrenes 4. Seeds ovoid, 6–7 mm long, ridged on the abaxial face, blackish brown when dry.

Distribution, habitat and phenology: — Lasianthus trongii is currently only known from Vietnam, occurring in provinces of Quang Binh and Quang Tri. It was found in secondary forests at elevation of 50– 100 m. Flowering and fruiting specimens were collected in November and December.

Etymology: —The new species is named in honor of Mr. Nguyen Dinh Trong who has made great contributions to local forest protection of the type locality in Quang Tri Province.

Vernacular name: —Xú hƯƠng trọng (Vietnamese).

Preliminary conservation assessment: — Lasianthus trongii is currently known from two localities in Quang Binh and Quang Tri Provinces, Central Vietnam. The Extent of Occurrence (EOO) is estimated less than 1,000 km 2 and the known Area of Occupancy (AOO) is 8 km 2. Two populations in Quang Tri and one population in Quang Binh were found in the understory of the broad-leaved evergreen forests, and each with 50 individuals were observed. In the population of Quang Tri, threats such as deforestation for charcoal and agricultural purposes have been observed, while the population in Quang Tri is inside the protected area of the national park and well-preserved. According to IUCN criteria B1a,b(iii), B2a,b(iii) and D, the species was assessed as Endangered (EN) ( IUCN 2024).

Additional specimens examined (paratypes): — VIETNAM. Quang Binh Province: Phong Nha-Ke Bang National Park, Phong Nhar Botanic Garden, in broad-leaved evergreen forest, 17.55657°N, 106.29983°E, 89 m elevation, 5 December 2024, S. Tagane, V. S. Dang, P. Souladeth, Q. T. Pham, T. Yamamoto, T. Fujiwara, R. Masuda, K. Souvannakhoummane, K. Phengmala N 934 ( FOF, KAG [ KAG 189037], VNM).

Notes:— It resembles L. tamdaoensis V.S.Dang in Dang & Naiki (2019: 51) which is known from Tam Dao National Park and Ba Vi National Park of northern Vietnam, but differs from that species in the several characters. This new species is also similar to L. kailarsenii Poopath, Vajrodaya & Napiroon in Napiroon et al. (2018: 208), a Thai species, but distinguished by its leaves 8–12 cm long (vs. 5–7 cm long), petioles 2–3 mm long (vs. 1 mm long), corolla tube 4–4.5 mm long (vs. tube 8–10 mm long), and fruits reddish-orange, ca. 10 mm in diam. (vs. blue, 3.5–5 mm in diam.). The comparison among Lasianthus trongii , L. tamdaoensis and L. kailarsenii is shown in Table 1.

Figures

FIGURE 1. Holotype of Lasianthus trongii V.S.Dang, T.A.Le & Tagane (LTA001, VNM). Photoed by Van-Son Dang.

FIGURE 2. Lasianthus trongii V.S.Dang, T.A.Le & Tagane, A. Habitat and habit, B. Flowering branch, C. Shoot apex, D. Abaxial leaf surface, E–G. Flower buds and flowers, H. Young fruit, I. Mature fruit, J. Pyrenes. Photoed by Le Tuan Anh.