Last May I was in Utah for the American Penstemon Society Meeting. The Monday after the meeting ended a group of us Penstemaniacs went on a day trip to find some very rare or unusual species of Penstemon. The one I found most intriguing was P. ammophilus. The species epithet translates to “sand-loving”, which is very accurate in that this species grows in sand dunes. We visited a site in southwestern Utah (Washington County, I think) that had a sand dune at the base of Navajo sandstone cliffs. The species was described in 1982 by Noel Holmgren and Leila Shultz, and presented a bit of a taxonomic conundrum. It is classified in subgenus Habroanthus section Glabri based on anther characters, but could also fit into subgenus Penstemon section Cristati based on other features.
Penstemon ammophilus is a sensitive species, occurring in just a couple of locations in Utah between 1539 – 2200 m (5050 –7216 ft). The plant grows in small clumps with the flower stalks staying under 30 cm (1 ft) in height. The flowers are 14-17 mm long (~ 1/2 inch) and light purple in color. It is not yet in cultivation, and I suspect it would be a real challenge to grow in the garden given it’s soil requirement of very deep sand.
Penstemon ammophilus is one of the most intriguing species of this large and very diverse genus. It has a unique characteristic of an inflated stem in the inflorescence, and the foliage is so glandular that it acquires a coat of sand particles, which effectively serves as armor plating – protecting the plant from sand blasting. It grows in a very open habitat in very deep sand. The other feature that is unlike other things I’ve seen is the staminode, which has short stubby purple hairs. Other species of Penstemon with bearded staminodes have yellow hairs.
While I was photographing P. ammophilus I noticed that it was being pollinated by a large bombylid fly (a very hairy species) and by a species of Osmia (one of the many different mason bees that specialize on Penstemon) – sometimes at the same time.