P. grandiflorus has petals (the corolla) that merge to form an inflated tube that measures 35–48 millimeters from base to opening.

The tip of the staminode curves backwards and is covered in golden yellow hairs that are up to half a millimeter long.

The dispute is over if Thomas Nuttall or Frederick Traugott Pursh should be credited for publishing the first description of the species and being able to name it under the principle of priority.

Nuttall is credited with writing the Catalogue of New and Interesting Plants Collected in Upper Louisiana, both have at times been listed as being published in 1813.

[7][8] The American botanist Francis W. Pennell was one of the most prominent of the advocates for crediting Nuttall and using the name Penstemon grandiflorus.

[10][11] In a 1956 paper in Rhodora, Arthur Cronquist and his coauthors made the argument that P. grandiflorus had been in use since 1829 and that in the interests of stability it should be retained.

[7] World Flora Online (WFO) has a confusing position listing both names as accepted in 2023.

[13][14] Disagreeing with these databases the Missouri Botanical Garden,[15] the USDA Natural Resources Conservation Service PLANTS database (PLANTS),[16] the Flora of North America (FNA),[2] and NatureServe[1] all list the species as Penstemon grandiflorus.

At that time it was evaluated with a conservation status of secure, G5 as they thought the global population was not significantly declining.

[4] It is found in a limited number of northern counties in Illinois and has been designated an endangered plant by the state.

[21][22] In areas with plains pocket gophers (Geomys bursarius) the numbers of Penstemon grandiflorus are reduced because they readily eat the plants.

In oak savannas fire is also an important force in maintaining suitable openings for plants like P. grandiflorus.

[25][4] A variety of shell-leaf penstemon with a wider range of flower colors from white to deep purple was developed by Denver resident Mary Anne Heacock.

Under the name "Prairie Jewell" it is promoted by the Colorado horticultural non-profit Plant Select.

[4] The Dakota people are recorded by the ethnographer Dilwyn J. Rogers as using the boiled root for chest pain.