N.Vietnam, Cao Bang Prov., Trung Khanh Distr., Ngoc Khe Municipality, Pac Nga village, around point 22º54'59''N, 106º31'44''E, at elevation 700-800 m a.s.l. Remnants of primary broad-leaved evergreen and coniferous forest along tops of rocky ridges and mesae composed with light gray solid marble-like highly eroded crystalline limestone. Lithophyte on very steep rocky mossy slope. Flowers dull olive-green, lip deep violet. Rare.