- USDA Plant Catalog – search by region, state and a number of categories. Actually this whole site is really good.
- Search in Google “[your state]” and “DA noxious weeds.”
- Thumb through wild plant guides for free on Google Books.
- There’s also the Native Plants Database, searchable by scientific name, region, etc.
- A number of universities have agricultural, landscaping and botanical sites where you can search for information specific to the region. Check out the sites of your local universities.
- Erowid allows you to cross reference entheogenic/drug information about plants.
- The very neat database Plants for a Future documents edible and medicinal plants specifically.
- The upper 500s, specifically the 580s in the library is the botanical section.
Be smart, be safe and enjoy!