Lasianthus bachmaensis V.S.Dang & Naiki, 2023

Dang, Van-Son & Naiki, Akiyo, 2023, A revision of the genus Lasianthus Jack (Rubiaceae) from Vietnam, Phytotaxa 581 (1), pp. 1921-1935 : 1921-1935

3. Lasianthus bachmaensis V.S.Dang & Naiki , sp. nov. — Fig. 17 (plate), Fig. 15 (map)

Type: — VIETNAM. Thua Thien Hue Province , Bach Ma National Park, 1183 m elev., 16°11’76.03’’N, 107°50’84.70’’E, in evergreen forest, 26 July 2019, Dang V.S. & Naiki A., Dang 406 (holotype VNM! [ VNM00042867 ]; isotypes VNM! [ VNM00042868 , VNM00042869 ], the herbarium of Iriomote Station (Japan)) .

Diagnosis: —This new species is morphologically similar to Lasianthus stephanocalycinus Naiki, Tagane & Yahara (2015: 173) based on leaf shape and fruit color, but differs from the latter in having smaller leaves (10–12 × 2–2.5 cm vs. 8–9.5 × 3–3.5 cm), shorter stipules (1–1.8 mm long vs. 2–3 mm long) and smaller calyx (1–1.5 mm long vs. 2 mm long for tubes and 1.5–2.5 mm long vs. 2.5–3 mm long for lobes).

Description: —Shrubs, evergreen, 1–2.5 m tall; branches and branchlets terete, 1–2 mm diam., appressedpubescent or strigose, internodes 1–3 cm long. Leaves opposite, blades elliptic or elliptic-lanceolate, 10–12 × 2–2.5 cm, coriaceous, yellowish brown when dry, adaxially glabrous, abaxially sparsely strigose on nerves, apex narrowly acute to acuminate, aristate 1–2 mm long, base cuneate or acute, margin entire; midrib slightly prominent adaxially, prominent abaxially; secondary veins 4–5 on each side of midrib, ascending at an angle of 40–60° from the midrib, curved to the margin, slightly distinct on both surfaces; tertiary veins parallel; petioles 3–5 mm long, appressed-pubescent. Stipules triangular, 1–1.8 mm long, persistent, densely pubescent. Inflorescences cymose, sessile or subsessile, 1–3-flowered; bracts small, 0.5–1 mm long, densely pubescent. Flowers fascicular or solitary, pedicel 1 mm long; calyx campanulate, 2–4 mm long, bluish purple, pubescent outside, calyx tube 1–1.5 mm long, calyx lobes 5, narrowly triangular, 1.5–2.5 mm long, tips acute or acuminate; corolla tube cylindrical, 5–8 mm long, white purple, corolla tube 3–5 mm long, pubescent outside, corolla lobes 5, triangular-lanceolate, 2–3 mm long, long-villose outside, floccose inside, the throat hairy; stamens 5, filaments short, anthers narrowly oblong, 0.5–0.8 mm long; ovary with 5 locules, style linear, 4–6 mm long. Fruits drupaceous, hemispheric, 4–5 mm long, 5–6 mm in diam., pubescent, crowned by 5 calyx lobes, orange when ripe; pyrenes 5. Seeds ovoid, 2–3 mm long, irregular sulcate on the abaxial face, brown when dry.

Other specimens examined: — VIETNAM. Thua Thien Hue Province , Bach Ma National Park, 1190 m elev., 16°11’76.13’’N, 107°50’84.75’’E, in evergreen forest, 26 July 2019, Dang V.S. & Naiki A., Dang 406a ( KYO!, VNM!, the herbarium of Iriomote Station (Japan )) .

Distribution: — Vietnam (known only from the Bach Ma National Park, Thua Thien Hue Province).

Habitat & Ecology: — This new species is currently known only from the type locality in Bach Ma National Park , Thua Thien Hue Province, central Vietnam where it grows well under the shade of the evergreen forest at an elevation between 1000–1200 m .

Phenology: —Flowering from March to August, fruiting from September to November.

Etymology: —The specific epithet refers to the type locality in the Bach Ma National Park, Thua Thien Hue Province, Central Vietnam.

Vernacular name: —Xú hưƠng bạch mã.

Preliminary conservation assessment: — Lasianthus bachmaensis is only known in Bach Ma National Park, Thua Thien Hue Province. The Extent of Occurrence (EOO) is less than 170 km 2 and the known Area of Occupancy (AOO) is less than 25 km 2. About 1000 individuals were observed along the roadside, streams, and edges of the evergreen forest which are easily affected by human tourism activities. Thus, we propose a status of Endangered (EN) according to the IUCN Red List Categories (IUCN 2019).

Notes: —This new species resembles Lasianthus stephanocalycinus Naiki, Tagane & Yahara (2015: 173) which is known from Bokor National Park of Cambodia and Hon Ba Nature Reserve of Vietnam, but differs from that species based on several morphological characteristics summarized in Table 1.

Figures

FIGURE 15. Distribution maps of Lasianthus annamicus, L. attenuatus, L. bachmaensis and L. bidoupensis.

FIGURE 17. Lasianthus bachmaensis V.S.Dang & Naiki (from the holotype, VNM): A. Branch with flower buds, B. Close-up of young branch and leaves, C. Stipules, D. Abaxial leaf surfaces, E–G. Inflorescence showing lateral view flower buds, H. Young fruit and buds, I. Mature fruits, J. Seeds.