I rarely spot mullein in Texas, or Maine which are the states where I soend most of my time. However, I see it all over the place driving from Texas to Maine or vice versa... so I usually collect it on the way. It’s not ideal to collect any plant from along a highway, however, because tire rubber breaks down into dust, that contains heavy metals that collects along roadsides. The metal is added to raise the melting temperature of the rubber. Apparently tires get up to about 200 degrees at hihway speeds and would not last long without metal additives.
There were 2 large Mullein plants on this property when I came here-I mow around them and any other native plants-now there are 7 huge Mullein plants that I harvest leaves from...
Here, if you have livestock, horses, etc you ruthlessly rip out any Datura you find so your assets on the hoof don’t eat it...