Southern blue flag is very similar to northern blue flag, and often confused. For anyone who is not a botanist, I'm not sure telling them apart is worth the trouble. Historically, they have at times been treated as one species even by science. But we have at least 34 species in northern North America, so it can be a lot of fun for wildflower nuts to track them down and puzzle them out. In earlier days, identification was important if you wanted to get the right medicine for your scrophulous sores or a variety of other maladies. This poisonous, readily available perennial plant was a sure thing for primitive medicine. The illustration here is a lighter colored flower than is typical.