FLORA OF VIETNAM Rubiaceae Ophyorrhiza sp. N. Vietnam, Thanh Hoa prov., Ba Thuoc distr., Co Lung municipality, territory of Pu Luong protected area, near Co Lung village (20°27′28′'N, 105°12′18′'E). Primary broad-leaved evergreen forest on very steep rocky slopes and cliffs of remnant highly eroded karst limestone ridge at elev. 450-550 m a.s.l. Terrestrial and lithophytic herb on very steep rocky slope. Flowers white, calyx dirty violet. Locally abundant.