Penstemon virgatus
Few genera are as synonymous with Western North America as penstemons or beardtongues. The genus is almost entirely native only to North America with the center of diversity falling west of the 100th meridian. Over 250 species are found in North America with one outlier in
Japan. The outlier is often placed in its own genus. Penstemons are native to every state in the union except Hawaii and almost every Canadian province besides Nunavut.
The genus is widespread in Mexico and found in Guatemala as well. To my knowledge, it is not native to any of the Caribbean Islands. Luckily for native plant lovers, diversity is centered in Utah and Western Colorado. Utah is home to almost 80 species and Colorado has more than 50 species. This means that most of them make excellent garden plants in Colorado.
Penstemon procerus
The Evolution of Penstemons
Penstemons are now placed in the Plantaginaceae (plantago) family. Genetic work discovered that they are more closely allied to those “weeds” found in compacted moist lawns and along trails than old world Verbascum (mulleins) and the somewhat similar looking Scrophularia (figworts). All penstemons have a tubular flower, which is why they were placed in the Scrophulariaceae family for more than 100 years. The tube can vary in length and color. The flowers are zygomorphic and bilabiate, meaning there are three lobes on the bottom of the tube and only two lobes at the top. Both the Latin name Penstemon and the common name beardtongue refer to a fifth sterile stamen. This stamen is called the staminode and does not produce any pollen. This staminode can have hairs on it giving it the appearance of a small woolly caterpillar. How the four fertile stamens dehisce (open) to release pollen has been used to differentiate closely-related species in the past. Examining how they open often requires a hand lens. Most species can be easily identified by their general appearance and habitat. In fact, habitat and range are strong clues to identify penstemons in the wild. Part of the reason there are so many species of penstemon is they have rapidly evolved in response to the multitude of habitat and microclimates in the Western US. Many species are rather closely related, but geographic isolation has allowed them to speciate or evolve into new species. Penstemon have been evolving to occupy almost every elevation and habitat in Colorado and the West. You will encounter penstemons from the plains to the peaks of the highest mountains. The only habitats they have been able to truly conquer are aquatic habitats and deep, dark shade in the forest.
Penstemon albidus, courtesy Mike Kintgen
The diversity of habitats and elevations is a win-win for gardeners. It means that regardless of growing conditions, there are at least a few species of penstemon suitable for your garden that will not need supplemental irrigation or amended soils. Are there any downsides to penstemons? Perhaps the only downside is that most penstemons are short-lived. Many species are pioneer plants by choice, colonizing recently disturbed areas such as landslides, burned areas, roadsides, and pipeline scars.
Great Places to see Penstemons
Penstemon nitidus, courtesy Mike Kintgen
Living in Colorado means that several to many species are a short drive from home. Starting near the northeast corner of the state, Pawnee Buttes is a great place to see Penstemon angustifolius and possibly P. eriantheris, though I have never seen it there. Mid- to late-May is the best time to view penstemons in flower. Also found in the Pawnee Buttes area is P. ambiguus, the most non- penstemon-like of our native species. It is found in the sand areas of the eastern Plains, in the eastern two tiers of counties.
Penstemon secundiflorus
Moving toward the southeast corner of Colorado – the area from Pueblo to the Kansas state line is home t several species. The bluff natural area west of Pueblo is good for P. angustifolius var. caudatus. If you are lucky, you can spot P. auriberbis as well. Further east out on the breaks and escarpments of Baca and Las Animas counties you can find P. buckleyu. I would love to see this species in bloom someday! I have only ever found the resting basal rosettes in winter and early spring. Late April and early May probably offer the best viewing for these areas. The foothills west of the urban strip can give spectacular displays of P. secundiflorus, P. virens, P. glaber, P. brandegeei (southern), and P. alpinus (south to Fremont county). The hogback right behind Littleton along C-470 can be blue and lavender with P. secundiflorus and P. virens in moist years. Coyote Ridge near Fort Collins has nice displays of penstemons, along with Lory State Park. Mid- to late- May is the best time to see these penstemons.
Penstemon glaber
Moving up into the mountains, two of my favorite places are Straight Creek on the west side of the Eisenhower Tunnel and Horseshoe Mountain in Park County. Visit these places in mid-to late-July depending on snow pack. Straight Creek has masses of P. whippleanus in multiple colors; and if you climb high enough, you can find P. harbourii in the screes. Horseshoe Mountain has both P. whippleanus and P. harbourii along with mass of P. hallii. You can see P. secundiflorus, P. glaber, P. virgatus, and P. rydbergii along the road-sides in South Park. These displays can be spectacular in the second week of July. Middle Park is one of my favorite places to view penstemons. Here, masses of P. caespitosus carpet slopes along US 40 and US 9. Penstemon cyanthophorus can be found along both US 9 and US 40. One spot along US 40 is just inside the Kremmling city limits. P. virgatus and P. glaber can be found on slopes along county roads. Plan on catching the show in late May to mid-June depending on how early or late a Spring we are having. North Park is special in its own way. It has P. cyanthophorus scattered amongst the sagebrush. I never find more than a few individuals. Penstemon secundiflorus and P. virens appear along with more P. virgatus. In 2005, a recently completed oil/gas line has become a ribbon of P. virgatus stretching off and on for miles in a bluish-purple road across the landscape. Sadly, I never stopped to take photos and by 2006 it was largely gone. June and early July are good to view penstemon in this area, depending on snow-pack.
If I had to pick one area to see the most species in one or two days, it would be Browns Park in far northwest Colorado. More than ten species have been reported. It was the site of the 2010 American Penstemon Society meeting. We saw the regional endemic P. yampanensis, P. scarious cyanomontanus, P. fremontii, P. humilus, P. angustifolius var vernalis, P. pachyphyllus var mucronatus and several other species.
Near the dump for the city of Grand Junction, Kenton Seth took me to see P. moffatii. It was beautiful on a rare rainy day in late April. Looking past the wind- blown trash there was a spectacular variety of Grand Valley native plants along with P. moffatti. It was a fun place to check one more of Colorado’s 56 species off the list.
Penstemon virens
Penstemons are a joy in the garden and even more so in the wild. I wish you happy penstemon finding this season.
Mike Kintgen is Senior Curator at Denver Botanic Garden Rock Alpine collection and a wester native plant researcher.
Reprinted with the author’s permission, from the April 2024 issue of Saximontana, the monthly newsletter of the Rocky Mountain Chapter of the North American Rock Garden Society.