It truly lives up to its species name — grandiflorus — this tall, showy, Large-flowered Beardtongue. What makes it even more impressive is that it grows in dense clumps along roadsides, preferring the sparsely colonized roadcuts.
Penstemon grandiflorus growing alongside the interstate in central MN.
It is known by many other names as well: Showy Beardtongue, Pink Beardtongue, Shell-leaf Beardtongue, Canterbury Bells, and Wild Foxglove. Large-flowered seems the most appropriate, though based on the size of its floral display.
Individual plants were at least 3 feet tall, making it one of the largest of the Penstemons, with flowers that were about 2 inches long and almost an inch wide.
These flowers should be very attractive to the queen bumblebees out foraging on early summer wildflowers.
As a testament to its adaptability and tolerance, Prairie Moon Nursery’s description of this species is: “prefers full sun to partial shade, dry-mesic to dry conditions, and poor soil containing rocky material or sand.”
It certainly seems to do well on highway embankments.
Back Yard Biology 
Looks a lot like our P. palmeri, and bumblebees like them both. Palmeri is easy to naturalize here; I have a big clump on a dry slope in the yard. Best of all: palmeri is extremely fragrant. I try to walk downwind as often as possible. I’ll put a photo on fb.
Interesting! I’ve tried to grow Penstemon in my garden, but the soil is too wet (clay not sand), and I probably fertilize too much for its liking.
I’ve always wondered what that beauty was growing roadside in June. Now I know. Thanks, Sue!
So glad I could help! Thanks for writing.
That’s a real beauty. I can’t remember ever seeing it here.
That’s gorgeous! We have several species of penstemons here but not that one. The large size of it is wonderful!