An order of flowering plants, division Magnoliophyta (Angiospermae), in the subclass Rosidae of the class Magnoliopsida (dicotyledons). The order consists of only the family Podostemaceae, with about 200 species, the greatest number occurring in tropical America. They are submerged aquatics with modified, branching, often thalluslike shoots; small, perfect flowers with a much reduced perianth; a superior ovary with united carpels and numerous small seeds without endosperm.