The USDA Plants Database is a rich source for a lot of information you'll need for this project
Search for plants -- use the scientific name for best results -- and find:
The government is the largest publisher in the U.S.
Federal, state and local governments gather data, provide consumer information and share research on important subjects like biodiversity.
Append “site:.gov” to a google search to limit your search results to government websites.
Example: "monarch butterflies" site:.gov