Two new species of Lasianthus Jack (Rubiaceae) from southern Vietnam Author Dang, Minh Quan School of Education, Can Tho University, 3 / 2 Street, Ninh Kieu District, Can Tho City, Vietnam. Pedo-Geography and Soil Resources, Institute of Geography (IG), Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Vietnam. Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Vietnam. Institute of Tropical Biology, Vietnam Academy of Science and Technology, 85 Tran Quoc Toan Street, District 3, Ho Chi Minh City, Vietnam. Iriomote Station, Tropical Biosphere Research Center, University of the Ryukyus, 870 Uehara, Taketomi-cho, Yaeyama-gun, Okinawa, 907 - 1541 Japan. dmquan@ctu.edu.vn Author Nguyen, Manh Ha havdl72@ig.vast.vn Author Hoang, Nghia Son hoangnghiason@yahoo.com&tho1010@gmail.com Author Nguyen, Thi Mai Huong ngmaihuong2008@gmail.com&quynhchihonguyen@gmail.com Author Truong, Ba Vuong bavuong2019@yahoo.com Author Dang, Van Son dvsonitb@gmail.com text European Journal of Taxonomy 2022 2022-03-18 806 19 31 journal article 20138 10.5852/ejt.2022.806.1697 28f53295-9155-4b84-ab43-45e852842817 2118-9773 6373945 Lasianthus sonlangensis V.S.Dang, Vuong & Quan sp. nov. urn:lsid:ipni.org:names:77295608-1 Figs 4–5 ; Table 2 Diagnosis Lasianthus sonlangensis sp. nov. is morphologically similar to L. caeruleus Pitard ( Fig. 6 ) which is endemic to Vietnam in the shape of leaves and inflorescences, but differs from the latter by having secondary veins 5–7 pairs (vs 4–5 pairs), petioles 2–3 mm long (vs 4–5 mm long), bracts present 0.6– 1 mm long (vs absent), calyx tube 1.5–2 mm long (vs ca 1 mm long), calyx lobes 0.7–1 mm long (vs ca 0.5 mm long) and corolla lobes 4 (vs 5). For a further comparison see Table 2 . Etymology The specific epithet is derived from commune ʻSƠn Langʼ where the new species was discovered. Vernacular name Xú hƯƠng ʻSƠn Langʼ. Type material VIETNAM • Gia Lai Province , K’Bang District , Son Lang Commune , Kon Chu Rang Nature Reserve , primary evergreen forests ; 14°29′15.08″ N , 108°32′11.10″ E ; at 900–1100 m a.s.l. ; 24 Apr. 2021 ; Van-Son Dang , Ba Vuong Truong , Minh Quan Dang & Nghia Son Hoang Dang 465 ; holotype : VNM !; isotypes : HN !, VNM !. Description Shrubs, evergreen, up to 1 m tall; branches and branchlets slender, 1–1.5 mm diam., glabrous, internodes 1.5–2.5 cm long. Leaves opposite, blades oblong to oblong-laceolate, 5–7 × 1–1.5 cm , coriaceous, yellowish brown when dry, glabrous on both sides, apex acute to acuminate, aristate 0.7–1 mm long, glabrous, base acute, margin entire; midrib slightly prominent adaxially, prominent abaxially; secondary veins 5–7 pairs, ascending at an angle of 60–75° from midrib, curved to the margin, flat adaxially, slighly prominent abaxially; tertiary veins subparallel to subreticulate; petioles 2–3 mm long, grabrous. Stipules triangular, 0.8–1 mm long, persistent, glabrous except barbate margin. Inflorescences cymose, sessile, 1–9-flowered; bracts small, 0.6–1 mm long, glabrous except barbate margin. Flowers sessile; calyx campanulate, 2–3 mm long, white to whitish purple, calyx tube 1.5–2 mm long, glabrous, calyx lobes 4, linear-triangular, 0.5–1 mm long, glabrous except barbate margin; corolla tube cylindrical, 8–9 mm long, white, corolla tube 6–7 mm long, puberulous outside in upper part, corolla lobes 4, triangular, 1.5–2 mm long, puberulous outside, floccose inside in the throat; stamens 4, filaments short, anthers oblong, 1–1.2 mm long; ovary with 4–5 locules, style linear, 7–8 mm long, stigma lobes 4, 0.4–0.7 mm long. Fruits not seen. Fig. 4. Lasianthus sonlangensis V.S.Dang, Vuong & Quan sp. nov. A . Branch. B . Stipule and flower bud. C . Abaxial leafs surfaces. D–F . Close-up of infructescence. G–J . Close-up of flowers. Photos by Ba-Vuong Truong on 24 Apr. 2021. Fig. 5. Lasianthus sonlangensis V.S.Dang, Vuong & Quan sp. nov. A . Branch. B . Abaxial and adaxial leafs surfaces. C . Stipule and flower bud. D . Infructescence. E . Flower view from above. F . Flower in side view. G . Flower in vertical section. H . Stigma. I . Stigma apical portion. Line drawings from the holotype ( Dang 465 ) by Ba-Vuong Truong. Fig. 6. Lasianthus caeruleus Pitard. A . Flowering branchs. B . Stipule. C . Abaxial leaf surfaces. D–E . Close-up of calyces, flower buds and young fruits. F . Close-up of inflorescences and flowers. Photos by Van-Son Dang on 26 Jul. 2019. Table 2. Comparison of Lasianthus sonlangensis V.S.Dang, Vuong & Quan sp. nov. and L. caeruleus Pitard. * = from Pitard 1924 ; ** = from Dang 411 , VNM.

Characters	Lasianthus sonlangensis sp. nov.	Lasianthus caeruleus
Leaf blades	5–7 × 1–1.5 cm	4.5–7 × 0.8–1.5 cm *
Secondary veins	5–7 pairs	4–5 pairs *
Petioles	2–3 mm long	4–5 mm long *
Stipules	persistent, 0.8–1 mm long	often deciduous *
Bracts	0.6–1 mm long	absent*
Calyx tube	1.5–2 mm long	ca 1 mm long *
Calyx lobes	0.7–1 mm long, 4-lobed	ca 0.5 mm long, 5-lobed *
Corolla tube	6–7 mm long	4–5 mm long **
Corolla lobes	1.5–2 mm long, 4-lobed	1.5–2 mm long, 5-lobed **

Distribution, habitat and phenology Lasianthus sonlangensis sp. nov. was discovered in Kon Chu Rang Nature Reserve, Gia Lai Province , southern Vietnam . It occurs in the understory of primary evergreen forest together with Lasianthus hirsutus (Roxb.) Merr. ( Rubiaceae Juss. ), Ardisia perpendicularis E.Walker ( Primulaceae Batsch ex Borkh. ), Mischocarpus sundaicus Blume ( Sapindaceae Juss. ), Pterospermum mucronatum Tardieu ( Malvaceae Juss. ) and Trivalvaria costata (Hook.f. & Thomson) I.M.Turner ( Annonaceae Juss. ), at 900–1100 m elevation. Flowering specimens were collected in April. Population and threats Lasianthus sonlangensis sp. nov. is currently known from only one locality with a small population of less than 10 individuals. The forest habitat where we found this species is frequently disturbed by anthropogenic factors, such as spontaneous tourism activities and collection of non-timber forest products (NTFPs).