N. Vietnam, Prov. Cao Bang, distr. Tra Linh, municipalite Quoc Toan, vicinity of Thang Heng and Lung Tao villages near Thang Heng lake at 500 m alt. Open clayey alluvial banks of karst lake periodically flooded with water. Prostrate herb in wet places. Flowers white. Abundant. Codominante on open places. VH 4931 25-27.05.1997 International Botanical Expedition of the U.S.A. National Geographic Society (grant No 5803-96)