There is a population of Palmer’s penstemon in Grand Canyon Park that are about half the size they are supposed to be according to almost all the field guides and web sites. I have verified that they are Penstemon palmieri. I have observed them on the rim near Hopi Point, and along the South Kaibab trail above about 6000 feet elevation. There is no individual taller than about 30 inches. By contrast, there is a population I am familiar with 100 miles to the south, on the ridge between Mingus Mountain and Woodchute Mountain, where most of the individuals are between 3 and 5 feet, which fits the field guides’ descriptions.
The Forest and Mountain Plants of Northern AZ field guide says there are 2 varieties of Penstemon palmieri, but gives no indication of a difference in height. The USDA website https://plants.usda.gov/plantguide/pdf/pg_pepa8.pdf says that according to an old book there are 3 varieties, but also gives no information:
Cronquist, A., A.H. Holmgren, N.H. Holmgren, J.L. Reveal, & P.K. Holmgren 1984. Intermountain Flora. Volume Four. Subclass Asteridae (except Asteraceae). The New York Botanical Garden, Bronx, New York.
The cheapest copies of Intermountain Flora volume 4 I can find go for $85. Can someone who has access to this book look up the information and post an image to this topic? I am not a naturalist, but it seems to me that a population that is uniformly smaller than another geographically isolated population perhaps should be considered a subspecies. Perhaps the accepted meaning of “variety” and “subspecies” has changed since Intermountain Flora was published.
I don’t know the extent of this population of small Penstemon palmieri. It seems that information on the “varieties” of Penstemon palmieri has been lost over time. It could be a research project for someone.