N. Vietnam, Prov. Quang Binh, distr. Minh Hoa, 72 km to NWW from Dong Hoi, municipalite Thuong Hoa, Yen Son village, limestone massif Ke Bang (N 17°40′ E 105°57′). In shallow water of small karst lake on alluvial valley bottom between limestone ridges and mesas at 200 m alt. Aquatic underwater plant with shoots up to 30 cm lg occurring on 0.1-1 m depth. Common and sometimes abundant. VH 4840 19.05.1997 International Botanical Expedition of the U.S.A. National Geographic Society (grant No 5803-96)