The USDA map means exactly that - it occurs in all the states and provinces coloured green, and the "N" under "Native status" means that it's native, not an introduced weed. The thing to keep in mind with these maps is that they are based on political boundaries, not actual plant ranges (which don't respect political boundaries, needless to say). The plant may not be present in the entire state or province; a plant often occurs only in certain habitat or at certain elevations, which is not indicated on these maps. By clicking on the states, you can get more info sometimes, i.e. the counties the plant has been found in.