I saw a cup plant, Silphium perfoliatum, the other day. I want it. Here is a GREAT picture of its uniqueness! Self-explanatory.
The one I saw is along the side of the highway by the oak grove. I want it! And I want its cousin, the compass plant, too, Silphium laciniatum. I already have Prairie dock in my yard, that's Silphium terebinthinaceum, and it's doing well for 5 or 6 years now, so everyone in the family should be together ... right? I have a case of the "wants" is all. I probably won't go digging it.
But if YOU see a lovely plant, I won't absolutely dissuade you from pillaging country roads for plants, just make sure you aren't taking an endangered or at-risk plant. Make sure! Know absolutely what you're doing! Especially: Know the laws in your county or state. Then if you're triple sure, and it's numerous, don't take everything out of the area, and make sure that you're leaving plenty behind.
Really, not too many people where I live seem to care about plants in the ditches. But I do have the experience of Joe Swagger Bluster Intimidation Cop ... but that's a long story.
If law enforcement talks to you while you're harvesting OR digging up a plant, be very, very respectful and cautious, or say as little as possible. Preferably both. That's my advice. And don't have any outstanding warrants, eh?
It is so much easier, safer and cleaner to order prairie natives from a reputable nursery, I officially recommend it.