Potamogeton clystocarpus is a rare species of flowering plant in the pondweed family known by the common name Little Aguja pondweed. It is endemic to Texas in the United States, where it is known only from one river canyon in Jeff Davis County. There is a single population of the aquatic plant in , and it has never been seen anywhere else. This is a federally listed endangered species of the United States. In 1991 and 1992 heavy flooding scoured the canyon and the plant has not been seen since. Surveys have not relocated the plant.