This is the corresponding site for the wetland plants of the western United States. 1988 National List of Plant Species that Occur in Wetlands . National Wetlands Inventory, U.S. Fish and Wildlife. From this page you can download a list of the plant species found in U.S. wetlands as a text file. The field structure is rather cryptic so be sure to download the information on the file structure of the database as well.
Regional lists are also available.
Center for Aquatic Plants . University of Florida. The Center for Aquatic Plants has a wealth of information on aquatic plants, both native and introduced, in Florida. Bureau of Aquatic Plant Management . Florida Division of State Lands.