A revision of the genus Lasianthus Jack (Rubiaceae) from Vietnam Author Dang, Van-Son 0000-0001-8681-4141 Iriomote Station, Tropical Biosphere Research Center, University of the Ryukyus, 870 Uehara, Taketomi-cho, Yaeyama-gun, Okinawa, 907 - 1541 Japan. & Institute of Tropical Biology, Vietnam Academy of Science and Technology, 85 Tran Quoc Toan Street, District 3, Ho Chi Minh City, Vietnam. & Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Vietnam. & dvsonitb @ gmail. com; https: // orcid. org / 0000 - 0001 - 8681 - 4141 dvsonitb@gmail.com Author Naiki, Akiyo 0000-0002-3235-2823 Iriomote Station, Tropical Biosphere Research Center, University of the Ryukyus, 870 Uehara, Taketomi-cho, Yaeyama-gun, Okinawa, 907 - 1541 Japan. & Iriomote Station, Tropical Biosphere Research Center, University of the Ryukyus, 870 Uehara, Taketomi-cho, Yaeyama-gun, Okinawa, 907 - 1541 Japan. & naiki @ lab. u-ryukyu. ac. jp; https: // orcid. org / 0000 - 0002 - 3235 - 2823 * Author for correspondence naiki@lab.u-ryukyu.ac.jp text Phytotaxa 2023 2023-01-26 581 1 1921 1935 http://dx.doi.org/10.1094/PDIS-04-22-0755-PDN journal article 10.11646/phytotaxa.581.1.1 1179-3163 7571550 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 .