FLORA OF LAOS Acantaceae Strobilanthes arborescens sp.nov. Luang Prabang prov., Pon Xay distr., Houay Man village, Phou Pak Sang Mountain, around point 19°59'03.8''N 102°25'09.0''E. Degraded primary evergreen and semideciduous forest on very steep rocky mountain slopes composed by solid marble like highly eroded limestone at elev. 1000-1150 m a.s.l. Deciduous treelet or shrub 2-4 m tall on open karstic rocks on mountain top. Flowers blue. Very common. Main co-dominant of deciduous scrub on open tops of karstic limestone mountains. LA-VN 2050 4 April 2017 Coll.: L.Averyanov, N.T.Hiep, N.S.Khang, C.Q.Ngan, T.Maisak, Vichith Lamxay, Koudkeo Phommachanh, Phizar Sayalath, Keooudone Souvannakhoummane.