Ecological Risk Screening Summary - Indian Swampweed (Hygrophila polysperma) - High Risk

Species that are considered high risk have a well-documented history of invasiveness in at least one location globally and are of establishment concern for the contiguous United States based on a climate matching analysis.

Hygrophila polysperma, Indian Swampweed, is an amphibious plant native to southeast Asia. H. polysperma is a popular species in the aquarium trade, which has likely led to the introduction and spread of this species globally. H. polysperma is listed as a Federal Noxious Weed and regulated in at least 14 U.S. States. H. polysperma has been introduced to and become established in the United States. It has also been introduced and become established in Australia, Europe, and Japan. Establishment in Europe has occurred only in thermally regulated waters. H. polysperma outcompetes, displaces, and reduces growth in native aquatic plants by forming dense monocultures. These dense populations negatively impact recreational areas and water control structures, and in turn have become an economic burden. The History of Invasiveness for Hygrophila polysperma is classified as High due to well documented nonnative establishment and negative impacts. The climate matching analysis for the contiguous United States indicates establishment concern for this species. The highest areas of climate match for Hygrophila polysperma in the contiguous United States were found in the south and southeast from Texas to Virginia. The Certainty of Assessment for this ERSS is classified as High due to evidence of nonnative establishment, as well as several peer-reviewed sources documenting negative impacts. The Overall Risk Assessment Category for Hygrophila polysperma in the contiguous United States is High.