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.
Canada's Aquatic Environments, Habitats . University of Guelph. An extremely impressive and informative web site on all aspects of Canada's aquatic habitats. You'll find pictures and information on the importance and biology of each species ranging from phytoplankton to vascular plants. Center for Aquatic Plants .