When little Elves have cut themselves,
Or Mouse has hurt her tail,
Or Froggies arm has come to harm,
This herb will never fail.
The Faeries skill can cure each ill
And soothe the sorest pain;
She’ll bathe and bind, and soon they’ll find
That they are well again.
Apparently Selfheal is used by elves and fairies as a cure-all. It was actually used by Native Americans for a number of medicinal uses. It seems like many species of the mint family have been used for medicine. This one is also edible, although I’ve never tried it.
This plant looks like a weed of lawns and other disturbed areas, but is actually native to most of North America. It must be one of those plants that colonizes disturbed areas and, since people disturb the land so much, it has become quite common.