Penstemon grandiflorus is in subgenus Penstemon section Coerulei (formerly Anularius).
This beautiful species is native to the Great Plains region of North America. My first encounter with it was while I was a graduate student at the University of Oklahoma. I was struck by its beauty, the size of the flowers, and how tall it grew compared to the penstemons I had first encountered in Oklahoma. It reaches to about a meter in height. The stems are sturdy, and the leaves are covered in a blush of wax, which makes the foliage a light bluish gray-green.
In the garden, this species tolerates dry conditions and requires well-drained soils. It’s pretty tolerant of most pH conditions, and it can tolerate partial shade. It can grow in Zone 4. Many members of the American Penstemon Society have reported success in growing this species in the midwest.