I tried keying this Penstemon to the species (Keil Key), but I’m a little rusty. This was my trail:
1′ Plants reproducing by seeds; spores produced but retained in ovules or developing into pollen grains.
2′ Ovules enclosed in an ovary at the time of pollination; the pollen-receptive structure a stigma; seeds borne in fleshy or dry fruits derived from ripened carpel tissue [ANGIOSPERMS].
3′ Gynoecium composed of 1 pistil, this either simple or compound.
4′ Perianth represented by 2 or more whorls or complete spirals , the outer usually treated as sepals and the inner as petals.
8′ Perianth parts usually in whorls of 4 or 5, or indefinite in number [MOSTLY DICOTS].
9. Petals connate into a ring or tube, sometimes only at the base, the entire corolla falling as a single unit.
10. Ovary or ovaries superior: KEY 9
Key 9: Dicots with Petals United into a Ring or Tube and a Superior Ovary
1′ Plants green and photosynthetic.
5′ Anther-bearing stamens as many as corolla lobes or fewer.
12. Functional stamens fewer than corolla lobes; staminodes sometimes present.
13′ Terrestrial plants, or if growing in water, leafy stems as well as flowers above water surface; underwater parts, if any, not finely dissected and trap-bearing; roots present; placentation axile, parietal, or basal.
14. Flowers actinomorphic or nearly so.
15. Corolla lobes 4: SCROPHULARIACEAE (I used this key in my botany classes. It’s worth noting Penstemon has been moved to Plantaginaceae)
Here I switch to my trusty Kearney and Peebles reference, Arizona Flora
“Plants annual or perennial, a few shrubby, in some genera partially parasitic; leaves opposite, alternate, or mostly basal, simple, entire to pinnately parted; flowers perfect, very irregular to nearly regular; calyx 4 or 5 toothed or lobed; stamens inserted on the corolla tube, commonly 4, in unequal pairs, a fifth stamen (staminode) often present but nonfunctional, or sometimes only 2 of the stamens perfect, or (in 1 genus) all 5 of the stamens perfect; style 1, the stigma entire or 2-lobed, the ovary superior, more or less completely 2-celled; fruit a capsule, usually 2 valved and longitudinally dehiscent, sometimes opening by pores or bursting irregularly; seeds usually many, small.
A large and diverse family, comprising many plants that are cultivated as ornamentals. The plants are mostly innocuous, but the Old World foxglove (Digitalis purpea), often grown in the U.S. as an ornamental, is the source of the drug digitalis, a powerful cardiac stimulant.”
Key to the Genera. I’m not going to bore you further with Flora and if you’re interested it really is worth buying the book. I love hiking, but sometimes it’s more fun when you are actively trying to identify plants (or animals if that’s your thing). I went as far as Penstemon.