N. Vietnam, Thanh Hoa prov., Ba Thuoc distr., Co Lung municipality, territory of Pu Luong protected area, near Co Lung village, Nui Doan (Pha Doan) mountain system (20°26′30′'N, 105°11′32′'E). Secondary open broad-leaved evergreen forest on steep rocky slope of remnant highly eroded karst limestone ridge at elev. 200-300 m a.s.l. Woody vine 10-12 m hg. Flowers white with violet tint, calyx dull pale. Not rare.