Lasianthus hoabinhensis V.S.Dang, T.S.Hoang & Naiki, 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 : 61-64

Lasianthus hoabinhensis V.S.Dang, T.S.Hoang & Naiki , sp. nov. Figures 3 & 4 .

TYPE:— VIETNAM. Hoa Binh Province: Da Bac District, Phu Canh Nature Reserve , in evergreen broadleaf forests, 20°55′08.00″N, 105°01′40.00″E ,, 1114 m elevation, 26 October 2021, T. S. Hoang, H. T. Nguyen, T. L. Ho & V. S. Dang HTS4215 (holotype VNM [ VNM00070335 !]; isotypes VAFS!, VNM [ VNM00070776 !]) .

Diagnosis: — Lasianthus hoabinhensis is closely related to L. attenuatus Jack (2012: 13) in having densely tomentose or setose on branches and axillary inflorescences, but it can be distinguished from latter by its leaf blades 15–25 × 5–8 cm (vs. 5–12 × 2.5–5 cm), secondary veins 9–11 pairs (vs. 6–8 pairs), calyx tube 3–4 mm long (vs. ca. 1 mm long) and lobes 7 (vs. 5), corolla lobes6 or 7 (vs. 5), 3–4 mm long (vs. 4–5 mm long), and pyrenes 6 or 7 (vs. 5).

Shrubs up to 3 m tall; branches ca. 5 mm in diam., densely tomentose or sometimes setose, blackish when dry; internodes 5–10 cm. Leaves opposite; blades oblong, oblong-ovate or elliptic-lanceolate, 15–25 × 5–8 cm, coriaceous, adaxially glabrous, abaxially tomentose, apex acute to cuspidate-acuminate, 10–15 mm long, base more or less oblique, slightly cordate, margin entire, midrib flat adaxially, prominent abaxially, secondary veins 9–11 pairs, ascending at the angle of 45–60° from midrib, curved to the margin, flat adaxially, prominent abaxially, tertiary veins subparallel, prominent abaxially; petioles 1–2 mm long, tomentose. Stipules narrowly triangular, 2–3 mm long, densely tomentose on both surfaces. Inflorescences axillary, cymose, up to 4-flowered, covered by persistent bracts. Bracts numerous, filiform, 8– 12 mm long, tomentose, forming a dense head. Flowers sessile, 16–20 mm long. Calyx obconical to campanulate, 4–6 mm long, hirsute, tube 3–4 mm long, pale-purple in vivo, lobes 7, linear, 2 mm long, hirsute on both surfaces. Corolla tube cylindrical, 12–14 mm long, tube 9–10 mm long, white, sparsely hirsute outside, lobes 6 or 7, ovate-triangular, 3–4 mm long, sparsely hirsute outside, villous inside. Stamens 6 or 7, inserted at corolla tube, filaments short, anthers oblong, 1.5–2 mm long. Ovary with 6 or 7 locules, style 15–17 mm long, glabrous, stigma 6- or 7-lobed, 0.5–0.8 mm long. Drupes subglobose to ovoid, 8–12 mm long, ca. 7 mm in diam., minutely hirsute, blue when ripe; pyrenes 6 or 7. Seeds ovoid, 2–3.5 mm long, smooth on the abaxial face, brown when dry.

Distribution, habitat and phenology: —The new species is only known from Phu Canh Nature Reserve, Da Bac District, Hoa Binh Province, Northern Vietnam. This species grows under the shade of the evergreen broadleaf forests, at an elevation of 1000–1200 m. Flowering and fruiting specimens were collected in October.

Etymology: —The new species is named after its type locality, Hoa Binh Province.

Vernacular name: —Xú hƯƠng hòa bình (Vietnamese).

Preliminary conservation assessment: — Lasianthus hoabinhensis is known only from a single population with about 100 individuals in Phu Canh Nature Reserve of Hoa Binh Province. A comprehensive survey of remaining forest near the type locality and neighboring provinces is needed to accurately investigate the distribution range and number of populations of the species. Due to lack of current data and according to IUCN criteria ( IUCN 2024), the species is assessed as “Data Deficient” (DD).

Notes:— The new species resembles L. attenuatus Jack (2012: 13) which is widespread in tropical and subtropical regions in Asia, but differs from that species in the several characters. Lasianthus hoabinhensis is also similar to L. pilosus Wight (2012: 75) , which is distributed in Malaysia and Thailand, but distinguished by its shorter petioles (1–2 mm long vs. 3–5 mm long), larger bracts (8–12 mm long vs. 4–5 mm long), smaller calyx (tube 3–4 mm long, lobes ca. 2 mm long vs. tube ca. 8 mm long, lobes ca. 5 mm long), and smaller corolla tube (9–10 mm long vs. ca. 15 mm long), and reddish-orange fruits (vs. blue). The comparison among L. hoabinhensis , L. attenuatus and L. pilosus is shown in Table 2.

Figures

FIGURE 3. Holotype of Lasianthus hoabinhensis V.S.Dang, T.S.Hoang & Naiki (HTS4215, VNM). Photoed by Van-Son Dang.

FIGURE 4. Lasianthus hoabinhensis V.S.Dang, T.S.Hoang & Naiki, A. Leafy branch, B. Stipule, C. Abaxial and adaxially leaf surfaces, D–F. Inflorescences and flowers, G–H. Mature fruits, I. Longitudinal section of fruit showing pyrenes. Photoed by Hoang Thanh Son.