N. Vietnam, Prov. Cao Bang, distr. Tra Linh, municipalite Quoc Toan, vicinity of Thang Heng and Lung Tao villages near Thang Heng lake. Dry broadleaved evergreen closed primary forest on steep slopes and bluffs of limestone ridges and mesas at 750-850 m alt. Epilite on vertical bluffs. Central sepal purple-violet, lateral sepals pale yellow, petals dull yellowish, lip brightly yellow. Abundant. VH 4897 25-27.05.1997 International Botanical Expedition of the U.S.A. National Geographic Society (grant No 5803-96)