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 73. Lasianthus vuquangensis V.S.Dang, Naiki & Yahara (2021:26) — Fig. 106 (plate), Fig. 104 (map) Type : — VIETNAM . Ha Tinh Province , Vu Quang National Park , 1130 m elev., 26 July 2015 , Yahara T. , Toyama H. , Tagane S. , Nguyen N ., Yang C.J., Nguyen H. V3806 ( holotype VNM ! [ VNM00042946 ]; isotypes DLU !, FU !, the herbarium of Iriomote Station ( Japan )) . Specimens examined: — VIETNAM . Central: Ha Tinh Province , Vu Quang National Park , 1130 m elev., 18˚15’34.07”N, 105˚20’47.01’’E, in lower montane forest, 26 July 2015 , Yahara T., Toyama H., Tagane S., Nguyen N., Yang C.J., Nguyen H. V3806 ( holotype VNM !; isotype DLU !, FU !, the herbarium of Iriomote Station (Japan)); in the same location, 1240 m elev., 18˚12’31.06”N, 105˚23’42.05’’E, in lower montane forest, 21 June 2016 , Yahara T. , Nguyen N. , Toyama H. , Tagane S. , Okabe N. , Nguyen H. V 5632 ( DLU , FU , the herbarium of Iriomote Station ( Japan )) . Distribution: —Endemic to Vietnam (known only from the Vu Quang National Park, Ha Tinh Province ). Habitat & Ecology: —Evergreen forest, in shaded places at 1000–1240 m elev. Phenology: —Flowering and fruiting from April to July. Vernacular name: —Xú hưƠng vũ quang. Notes: — Lasianthus vuquangensis is similar to L. rhinocerotis Blume (1826: 996) in the branches and branchlets densely brown-villous, the shape of leaves and calyx lobes 6, but differs from the latter in having smaller leaves (7–10 × 1.5–2.5 cm vs. 9–18 × 3–6.5 cm ), fewer secondary veins (5–6 on each side of midrib vs. 9–12 on each side of midrib), bracts 1–2 mm long (vs. 6–15 mm long), smaller calyx lobes ( 1–2 mm long vs. 3 mm long), larger corolla tubes ( 6–8 mm long vs. 4 mm long) and fruits with 6 (vs. 5) pyrenes. It is also similar to L. rhinocerotis subsp. pedunculatus (Pit.) H.Zhu (1998: 154) which is distributed in China and Vietnam , but differs from the latter in having smaller leaves (7–10 × 1.5–2.5 cm vs. 15–21 × 4–7 cm ), fewer secondary veins (5–6 on each side of midrib vs. 9 on each side of midrib), bracts 1–2 mm long (vs. 6–12 mm long), smaller calyx lobes ( 1–2 mm long vs. 3 mm long), larger corolla tubes ( 6–8 mm long vs. 4 mm long) and fruits with 6 (vs. 4–5) pyrenes.