In Illinois, it is illegal to take ANYTHING from State Parks. Seeds, plants, rocks, sticks, whatever. I work at a State Park, part time on a volunteer basis. They don't even let volunteers take seeds, let alone plants. You can collect from Federal lands(national forests, national monuments) with a permit. It is illegal to collect from roadsides, unless you've got written permission from the state. Which is a pain in the butt to get, but can be obtained after many hours on hold.
Some National Park employees have taken to accompanying "students" to sites that contain rare/endangered plants because these "students" had a tendency to over-collect the plants that they wanted to "study".
The only place you can collect without a permit is private property, but you must, of course, have the owner's permission. A former member here had some school/do gooder go thru her woods and "rescue" all her trillium grandiflorum. Which she had bought and planted.
If the collector doesn't have a permit or permission, the collector is stealing, plain and simple. and can be arrested and prosecuted, which they should be..and I don't care if the bulldozer is sitting right there.
People who just go out and dig up whatever, whenever really give legitimate plant rescue groups(like the Wild Ones)a bad name, and make it harder for them to do their job. Just IMO.