USDA. 2013. Weed Risk Assessment for Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine (Hydrocharitaceae) – South American spongeplant. United States Department of Agriculture. Animal and Plant Health Inspection Service. October 17, 2013. Version 4 : https://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/wra/Limnobium_laevigatum_WRA.pdf