Today’s featured penstemon is another one I photographed during the 2013 American Penstemon Society meeting. The Monday field trip was to Hell’s Canyon, where Penstemon triphyllus occurs in basalt cliffs at around 488 m (1600 feet) elevation. The range for P. triphyllus is the Snake River drainage from Hell’s Canyon through the confluence of the Columbia River and downstream towards the Columbia River Gorge. The plant is a subshrub that is rather sprawling. It flowers early to mid-summer (May – July).
Penstemon triphyllus is a member of subgenus Saccanthera section Saccanthera subsection Serrulati. I like to abbreviate this taxonomy as S3, but that’s just me being a nerdy plant systematist. I recently did an article about another member of S3, Penstemon glandulosus var. glandulosus, which was also one that we visited during the Hell’s Canyon trip. These two species share serrated leaf morphology, but are not very similar in overall appearance. The leaves of P. glandulosus are broadly ovate, whereas the leaves of P. triphyllus are narrowly lanceolate. The “triphyllus” epithet suggests there are three leaves per node. Mostly this is the case, but one often sees four leaves per node and sometimes one or two.
The closest relative to P. triphyllus is P. diphyllus, which occurs in western Montana and eastern Idaho. Whereas P. triphyllus is adapted to xeric conditions, P. diphyllus is found in habitats with more moisture. These two taxa were originally designated as individual species, but Keck (1932) lumped them as varieties of P. triphyllus. The American Penstemon society recognizes them as separate species. The next closest relative is P. richardsonii, which is found in central Oregon and Washington.
Penstemon triphyllus does well in the garden, but needs to be cut back in late summer to avoid becoming a straggly member of the flower bed.
Here are some other photos of this lovely species: