Smooth Beardtongue, Foxglove Beardtongue, Foxglove Penstemon
Synonyms of Penstemon digitalis: Chelone digitalis (Nutt.) Sweet, Penstemon alluviorum Pennell, Penstemon laevigatus subsp. alluviorum (Pennell) R.W.Benn., Penstemon laevigatus subsp. digitalis (Nutt.) R.W.Benn., Penstemon laevigatus var. digitalis (Nutt.) A.Gray
According to Plants of the World Online, Penstemon digitalis Nutt. is the correct and accepted scientific name for this species of Penstemon. It was named and described as such by Thomas Nuttall in Transactions of the American Philosophical Society in 1835. Some websites and databases (World Flora Online, Tropicos, the USDA Plants Database, etc.) list the scientific name as Penstemon digitalis Nutt. ex Sims, being described as such by John Sims in the Botanical Magazine in 1925 using a previous description by Mr. Nuttall… If you go by date, that would be correct. The International Plant Names Index (IPNI) has a record of both.
The genus, Penstemon Schmidel, was named and described as such by Casimir Christoph Schmidel in Icones Plantarum in 1763.
Plants of the World Online lists 276 species in the Penstemon genus (as of 3-26-20 when I am updating this page). The genus us a member of the Plantaginaceae Family with a total of 105 genera. Those numbers are likely to change.
The above distribution map of Penstemon digitalis is from Plants of the World Online. Areas in green are where the species is native and purple where it has been introduced. The map on the USDA Plants Database for North America is the same.
There are several links at the bottom of the page for further reading and help with positive ID.
Penstemon digitalis is a perennial wildflower that attracts several species of insects. I don’t have this species growing on my farm, but I found a few fairly large colonies growing along a highway close to town. It is quite a sight.
Plants grow to 3’ tall, more or less, on stems that are mostly hairless (glabrous). The leaves grow in an alternate pattern along the stems and sometimes in whorls of three. Leaf shape is variable but are mostly lance-shaped.
The white flowers are tube-shaped and the corollas are divided into a lower lip with 3 lobes and an upper lip with 2 lobes. The colony I photographed had all white flowers but they can also be splashed with purple.
I first identified this species as Penstemon tubaeflorus, but a member from iNaturalist suggested they were P. digitalis. The lobes on P. tubaeflorus flowers are closer together than those of the P. digitalis otherwise they are pretty much alike. I am sure there are other characteristics that separate the two species if you want to get down to the nitty-gritty.
You can check out the links below for better ID information. In 2020 I will revisit the colony and get more photos so I can write better descriptions.
There are several cultivars of Penstemon digitalis available.
I have enjoyed photographing and learning about the many wildflowers growing on the farm and other areas. My farm is in Windsor, Missouri in Pettis County (Henry County is across the street and Benton and Johnson aren’t far away). I have grown over 500 different plants and most have pages listed on the right side of the blog. I am not an expert, botanist, or horticulturalist. I just like growing, photographing and writing about my experience. I rely on several websites for ID and a horticulturalist I contact if I cannot figure them out. Wildflowers can be somewhat variable from location to location, so sometimes it gets a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.
I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at email@example.com. I would enjoy hearing from you especially if you notice something is a bit whacky.
NOTE: Plants of the World Online is the most up-to-date database. It is very hard for some to keep with name changes these days so you may find a few discrepancies between the websites. Just be patient. Hopefully, someday they will be in harmony. 🙂