FLORA OF LAOS Acanthaceae Strobilanthes arborescens sp.nov. Luang Prabang prov., Pon Xay distr., along the way to Bane Phou Souong village, Pha Hiua Bin Toc Mountain, around point 19°57'37.0''N 102°25'03.0''E. Degraded primary evergreen and semideciduous forest on very steep rocky mountain slopes composed by solid marble like highly eroded limestone at elev. 600-850 m a.s.l. Deciduous treelet 2-5 m tall and to 15 cm DBH on open rocky mountain top. Flowers blue. Very common. Main co-dominant of primary scrub on open rocky mountain tops. LA-VN 2157 5 April 2017 Photos Coll.: L.Averyanov, N.T.Hiep, N.S.Khang, C.Q.Ngan, T.Maisak, Vichith Lamxay, Koudkeo Phommachanh, Phizar Sayalath, Keooudone Souvannakhoummane.