Two distinct introduced Hydrilla verticillata biotypes exhibiting different reproductive traits (see below) occur in the United States. The dioecious southern form found in Florida appears to have originated from the Indian subcontinent, while the monoecious northern form (occurring north of North Carolina) appears to be derived from stock originating in Korea (Schmitz et al. 1991, Madeira et al. 1997).Hydrilla occurs in freshwater throughout most of peninsular Florida. Florida Exotic Pest Plant Council (FLEPPC) collection records confirm the presence of Hydrilla verticillata in Volusia, St. Lucie, Martin, and Palm Beach counties. Although not reflected in the FLEPPC records, collection records from the UF/IFAS Lakewatch water quality monitoring program and elsewhere suggest hydrilla is also widespread in freshwater systems within Brevard and Indian River counties.