If you live in the United States, you should know about the USDA Plants Database! ( plants.usda.gov )
Identifying what plants are actually native to your area can be surprisingly tricky. A lot of info out there is state- (or even less helpfully, region-) specific, but if you live in a large and/or geographically diverse state what's native in one corner may be completely foreign in another. There's also a lot of information out...