Photographed at Shaw Nature Reserve in August of 2020, this is the white form of Cirsium discolor, the pasture thistle.
Cirsium discolor (Pasture Thistle)
"What a thousand acres of Silphiums looked like when they tickled the bellies of the buffalo is a question never again to be answered, and perhaps not even asked." -Aldo Leopold
A Thousand Acres of Silphiums 