I favor wildflowersearch.org now for my first stop in field ID or species range related things. The database pulls from numerous sources of data, some I think were already mentioned here. Not only do they provide a range map which highlights the native and non-native range of the plant in the States.. It also gives pictures and links to the sources the data was generated from, some of which have detailed information related to habit, uses, and community. My only real issue so far is sometimes I have to clear the location to actually match up an identification of a non-native species that has moved into an area. You can manipulate and play with the way the data is pulled in so many ways.. Seems like it only gets better.
https://wildflowersearch.org/
