I just got back from the 2014 American Penstemon Society meeting, which was based in Springdale, Utah – the gateway to Zion National Park. We saw several species that occur in a very narrow range of distribution, but the highlight for me was Penstemon petiolatus. In the 2006 paper my lab published on the phylogeny of Penstemon, this was the only plant that was missing in terms of taxonomic representation of subsections.
When I first saw this species, it reminded me of Penstemon rupicola – a member of subgenus Dasanthera, which grows in basalt outcrops. This habit, growing out of rock faces, is a convergence between distantly related species. Penstemon petiolatus grows to about 10 cm (six inches) in height and the clump may be up to 60 cm (two feet) in diameter. It is a lovely rock garden plant, tolerant of cold and drought. It does need full sun to thrive.
Penstemon petiolatus is subgenus Penstemon, section Peltanthera, subsection Petiolati. It is the only member of Petiolati, and its taxonomic affinities are still not clear (personal communication, Noel Holmgren). It is certainly not like any of the other members of section Peltanthera. For example, it is the only species of this group that occurs only in limestone outcrops, growing in cracks and crevices of cliffs and ledges. It is also the only species in the group having leaves with distinct petioles, and it is the only one that is distinctly woody. Penstemon petiolatus was first found in the Sheep Mountains of Nevada, but is also found in a small area of the eastern Mojave Desert in Nevada, Arizona, and Utah. The site I visited was in the Beaver Dam Mountains of Utah. The elevational range of the species is 609 m to 1707 m (2000 ft to 5600 ft).
It is definitely a beautiful species of Penstemon, and my new favorite (at least for awhile…).