Botany on the Byways: Penstemon

Penstemon grandiflorus at Hitchcock Nature Center (photo by Seth Brooks)

Two types of penstemon can be found in western Iowa, Penstemon grandiflorus and Penstemon digitalis. The former, commonly known as large-flowered beardtongue, can be found in most counties in western Iowa. According to Iowa Prairie Plants, foxglove beardtongue (Penstemon digitalis) can be found in Fremont and Guthrie counties. Both species bloom into the month of June.

Penstemon grandiflorus

Penstemon species are commonly called beardtongue because of an interesting adaptation to attract pollinators. "One of the five stamens is sterile and does not produce pollen. It is often modified into a hairy or bearded tongue and probably attracts insects," as noted in the field guide Wildflowers of Iowa Woodlands by Sylvan Runkel and Alvin Bull.

Penstemon grandiflorus is common on Loess Hills prairies in western Iowa but very infrequent elsewhere on dry, sandy prairies and stabilized sand dunes. Its purple flowers bloom from late May to mid-June.

​Penstemon digitalis is frequent in moist, sandy soils on prairies and in other open places in southeastern Iowa, becoming very infrequent to the north and west. Penstemon digitalis is about the same height as Penstemon grandiflorus, but the leaves are somewhat larger and narrower. Penstemon digitalis also blooms slightly later than P. grandiflorus, from early to late June.

​Penstemon digitalis

Penstemon grandiflorus

Penstemon grandiflorus

Penstemon grandiflorus