N. Vietnam, Tuyen Quang prov., Na Hang distr., Thanh Tuong municipality, near Ban Bung village (22°16′26′'N, 105°25′58′'E). Primary broad-leaved evergreen wet forest on very steep limestone slopes of highly eroded remnant limestone ridge at elev. 700-750 m a.s.l. Lithophyte herb on wet mossy vertical limestone cliffs. Flowers blue. Very common.