It points out that they are not actually native to this country, but were imported here from China, back in the 1800's. So they've been here a long time and they have naturalized, so they grow wild all over the place.
We just had a thread from someone asking how to get rid of them. They do spread fairly fast.
They are Daylilies, Hemerocallis fulva, a species daylilly scattered all over the country in every state (I think even in the two not contiguous). They are tough and will spread and make a good ground cover. Not everyone is fond of them--the hybridizers seem to look down on them and have named over sixty thousand varieties and have changed the form into shapes and colors you would not believe. But I have always liked them because they seemed to be around every farmhouse and mark many former farms and cellars and former sites where people settled-some woman must have passed them along and carried them to every new farm. They do not form seed because of a genetic difference, the are triploid---well I am tired and it's late so I will not go into an essay ---google daylilies and you should find several daylily gardens that sell the species. I would not spend hundreds on some of the new varieties but , who knows, you might like them. Weedy