A checklist of the vascular plants of New England. 1988 National List of Plant Species that Occur in Wetlands . National Wetlands Inventory, U.S. Fish and Wildlife. 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.
Bryophyte Names List . Missouri Botanical Garden. Downloadable zipped files containing the family, genus, and species group names of the bryophytes of the Western Hemisphere including North America. The files are large. New World Grasses Catalog .