Northern Vietnam, Ha Tinh Prov., Huong Son Distr., Son Kim Municipality, in the vicinity of Rao An village, around point 18°22′00′'N, 105°13′13′'E. Primary evergreen lowland seasonal broad-leaved forest on granite rocky shady slopes of river valley at 260-360 m a.s.l. Herb vine 4-6 m lg in open place. Flowers light greenish. Not rare.