The genus Penstemon is endemic to the new world, predominantly in North America. The genus is particularly prevalent in the Western United States, and comes in a range of colors from light pink to blue. One of the best collections of Penstemon is at the Flagstaff Arboretum, and the best time to visit is during their annual Penstemon festival in July.
Penstemon rydbergii falls in the violet/blue color category of this diverse genus. The tubular flowers congregate in groups either forming circles or even spheres of flowers. We planted this one in the garden last year, and it has formed a lovely mound of blossoms.
Depending on the growing conditions where Penstemon rydbergii is found it can appear to be a completely different species than what your eye is trained to know. Sometimes the flowers are white and clustered together very tightly, where others are violet and loosely arranged. Perhaps this variety within the species is why Aven Nelson named this plant after Per Axel Rydberg. Rydberg was a well known botanist of his time, famous for naming new species over minor morphological differences instead of placing it as a subspecies. Very clever A. Nelson.
For those of you still not sure about wanting this lovely plant in your garden, consider this: Penstemons are known as excellent host plants for Castilleja species. Castillejas are hemi-parasitic which means they form specialized roots called haustoria roots that attach themselves to a host plant. They can survive without a host, but are especially vigorous with a host.