Lasianthus kbangensis V.S.Dang, Vuong & Naiki, 2022

Nguyen, Dinh Hiep, Dang, Minh Quan, Le, Ngan Thi Kim, Quach, Van Toan Em, Pham, Van Ngot, Le, Van Tho, Truong, Ba Vuong, Naiki, Akiyo & Dang, Van-Son, 2022, A new species of Lasianthus (Rubiaceae) from Kon Chu Rang Nature Reserve in central highlands of Vietnam, Phytotaxa 541 (3), pp. 291-296 : 292-295

Lasianthus kbangensis V.S.Dang, Vuong & Naiki , sp. nov. ( Figures 1 , 2 )

TYPE:— VIET NAM. Gia Lai province, K’Bang district, Kon Chu Rang Nature Reserve , in primary evergreen forests, 14°29’17.00”N, 108°32’16.14”E, 1015 m elevation, 20 April 2021, Van-Son Dang, Ba Vuong Truong, Ngoc Minh Tam Thao Duong, Ngan Thi Kim Le & Dinh Hiep Nguyen, Dang 463 (holotype VNM! [barcode VNM00045839]; isotypes HN! VNM! [barcode VNM00045840]) .

Diagnosis: — Lasianthus kbangensis is similar to L. oblongilobus H. Zhu (2002: 400) in their shrub habit (to 2.5 m tall), smooth on branches and branchlets, and glabrous leaves, but differs in having larger leaf blades (13–20 × 3–5 cm vs. 7–9 × 2–3 cm), longer petioles (10–13 mm long vs. 5–10 mm long), calyx lobes 4 and 0.5–1 mm long (vs. 5 or 6 and 2 mm long), corolla tubes 3–3.5 mm long (vs. ca. 5 mm long), and blue (vs. yellowish-orange) fruits when ripe ( Table 1 ).

Shrubs, evergreen, up to 2.5 m tall; branches and branchlets terete, 2–4 mm in diam., glabrous, blackish when dry; internodes 2–4 cm long. Leaves opposite; petioles 10–13 mm long, smooth, glabrous; blade elliptic, ellipticoblong to elliptic-lanceolate, 13–20 × 3–5 cm, coriaceous, glabrous on both surfaces, base cuneate, margin entire, apex acuminate and mucronately cuspidate; midrib flat adaxially, prominent abaxially; secondary veins 5–7 pairs, ascending at an angle of 45–50° from the midrib, curved to the margin, flat adaxially, slightly abaxially; tertiary veins subparallel to reticulate, flat on both surface. Stipules narrowly triangular, 0.8–1 mm long, glabrous except barbate margin. Inflorescences axillary, cymose, 5–13-flowered; bracts inconspicuous. Flowers sessile or subsessile; calyx campanulate, 2–3 mm long, white to purple, subglabrous, calyx tube 1.5–2 mm long, calyx lobes 4, linear to oblong, 0.5–1 mm long, sparsely strigose outside, glabrous inside; corolla salverform, 4–5 mm long, white, corolla tube 3–3.5 mm long, glabrous to sparsely strigose, lobes 4, triangular-lanceolate, 1–1.5 mm long, sparsely strigose outside, villous at throat inside; stamens 4, filaments short, anthers linear to oblong, 0.7–1 mm long; ovary with 4 locules, style linear, 2–3 mm long, glabrous, stigma with 4 lobed, 0.5 mm long. Fruit drupaceous, obovoid to subglobose, 8–10 mm long, 6–8 mm in diam., glabrous, crowned by 4 calyx lobes, blue when ripe; pyrenes 2(–4). Seeds ovoid, 5–5.5 mm long, 3–4 mm in diam., irregular sulcate on the abaxial face, blackish brown when dry.

Distribution and habitat: — Lasianthus kbangensis is currently known only from the type locality Kon Chu Rang Nature Reserve, Gia Lai province, Vietnam. It grows under the shade of the primary evergreen forest at elevation of 1000–1100 m, where Elaeocarpus kontumensis Gagnep. , Castanopsis harmandii Hickel & A.Camus , Lithocarpus pierrei (Hickel & A.Camus) A.Camus , Cinnamomum verum J.Presl , Garcinia sp. , Litsea elongata (Nees) Hook. f., Ardisia conspersa E.Walker , Antidesma montanum Blume are dominant.

Phenology: —Flowering and fruiting specimens were collected in April.

Etymology: —The new species “ kbangensis ” derives its name from the type locality Kbang District of the Gia Lai Province, where this species was discovered.

Vernacular name: —Xú hƯƠng kbang.

Preliminary conservation assessment: — Lasianthus kbangensis was only discovered in Kon Chu Rang Nature Reserve, Gia Lai Province. The Extent of Occurrence (EOO) is less than 150 km 2 and the known Area of Occupancy (AOO) is less than 20 km 2. About 500 individuals were observed from our field. Therefore, we propose a status of Endangered (EN) according to the IUCN Red List Categories ( IUCN 2019).

Discussion:— Lasianthus kbangensis is also similar to Paralasianthus hainanensis (Merrill) H. Zhu (2015: 277) , which was a combination based on Lasianthus hainanensis Merrill (1922: 355) (synonym: Saprosma merrillii H.S. Lo (1993: 15)) by Zhu (2015), in the shape of leaves and axillary inflorescences, but differs from the latter by having less secondary veins (5–7 pairs vs. 14–15 pairs), shorter stipules (0.8–1 mm long vs. 2–3 mm long), calyx tube 1.5–2 mm long (vs. ca. 1 mm long), corolla tube 3–3.5 mm long (vs. 4–4.5 mm long), and ovary with 4 locules (vs. 2 locules) ( Table 1 ).

Figures

FIGURE 1. Holotype of Lasianthus kbangensis V.S.Dang, Vuong & Niki (Dang 463, VNM) (photos by Van-Son Dang).

FIGURE 2. Lasianthus kbangensis V.S.Dang, Vuong & Naiki, A. Habitat and habit, B. Flowering and fruiting branches, C. Expanding young leaves, D. Abaxial leafs surfaces, E. Stipule, F–H. Inflorescences and flower buds, I–J. Young fruits, K. Mature fruit, L. Pyrenes (photos by Van-Son Dang).