Plants Database: plant list of attributes, names, taxonomy and symbolsProvided by the U.S. Department of Agriculture, Natural Resources Conservation Service. In an effort to avoid duplication of effort among government agencies this database supplies information on "the vascular plants, mosses, liverworts, hornworts, and lichens of the U.S. and its territories." It is a very rich database with numerous ways to search: by plant name (common or scientific), by state, by topic and others. Images, distribution of the plant, and classification of the plant are included.
This should be a resource you should learn and use!