I believe the Earthy trait is supposed to help you find "better" herbs. Something that I noticed was that usually, only one hero has to Discover, and then any other heroes automatically know what that is -- except that sometimes they don't, and when they Discover the plant, I think it becomes a rarer type of herb. That definitely needs to be tested more or confirmed by someone else. But if that's right, then I would think that's the Earthy trait coming into play.
I do know for sure that the Electrum that is by the cemetery isn't Electrum for all my heroes.
EDIT: @Ricalynn- Well I guess that's my problem, then! I'm not collecting the herbs every time.