Northern Vietnam, Ha Tinh Prov., Huong Son Distr., Son Kim Municipality, in the vicinity of Rao An village, around point 18°24′30′'N, 105°13′13′'E. Remnants of primary evergreen lowland seasonal broad-leaved forest on very steep granite/shale slopes of rocky river canyon at 180-200 m a.s.l. Woody vine 15-25 m hg in open river cliff. Flowers purple-violet, central tepal white with greenish center. Common. Usual co-dominant of liana non-strata vegetation all over the area.