Foxglove Penstemon
Penstemon digitalis
Snapdragon family (Scrophulariaceae)

Description: Prior to developing an inflorescence, this native perennial plant consists of one or more rosettes of basal leaves that are clustered together. They are medium green, sometimes with reddish tints. They are variable in shape, but tend to be ovate, obovate, or broadly lanceolate, and are up to 6" long and 2½" wide. Their margins are usually smooth. One or more flowering stalks emerge from the clustered rosettes during the spring, which are about 3' tall. They are hairless and light green, while the opposite leaves on these stalks are more lanceolate in shape than the basal leaves. Their edges often have tiny teeth, and the leaf surface is often shiny. The white flowers occur in a panicle at the top of each flowering stem, and bloom during late spring or early summer for about a month. They are tubular in shape and about 1" long, with the corolla divided into a lower lip with 3 lobes and and an upper lip with 2 lobes. Somtimes there are fine lines of violet within the corolla, which function as nectar guides to visiting insects. There is no floral scent. The entire plant is hairless, except on the outer surface of the flowers. The flowering stalk eventually turns dark brown, developing numerous oval seed capsules, each containing numerous seeds. These seeds are gray, finely pitted, and irregularly angled. This inflorescence eventually falls over are the seeds have formed, helping to distribute them, but the basal leaves remain. The small seeds can also be carried aloft by the wind for short distances. The root system has short rhizomes, which often produce new plantlets around the base.

Cultivation: The preference is full or partial sun, average levels of moisture, and loamy soil. This plant matures quickly during the spring, and the flowering stalks often ascend above neighboring plants. It adapts well to cultivation, is not bothered by disease, and is easy to grow. Under severe drought conditions, however, the leaves may turn yellow and the plant will wilt.

Range & Habitat: Foxglove Penstemon occurs occasionally, except in some counties of central and NW Illinois, where it is uncommon or absent. However, in other areas, it may be locally common. Habitats include mesic black soil prairies, openings in upland and floodplain forests, woodland borders, thickets, savannas, acid gravel seeps, pastures, and abandoned fields.

Faunal Associations: The tubular flowers of this plant attract long-tongued bees, including honeybees, bumblebees, Anthophorine bees, Miner bees, Mason bees, and large Leaf-Cutting bees. To a lesser extent, Halictid bees, butterflies, Sphinx moths, and hummingbirds may visit the flowers, but they are not effective pollinators. The caterpillars of the moth Elaphria chalcedonia (Chalcedony Midget) feed on the foliage of this and other beardtongues. There have been reports that the caterpillars of the butterfly Euphydryes phaeton (Baltimore) feed on the foliage of various beardtongues, but this does not appear to be the case in Illinois. The seeds are not often eaten by birds, nor is the foliage an attractive source of food to mammalian herbivores, although they may browse on it when little else is available.

Comments: This is probably the easiest Penstemon sp. to grow in areas that lie east of the Mississippi river. The flowers are quite showy, and the plant is large enough to compete against many kinds of weeds. Another desirable feature is that the blooming period is rather long for an early season plant. Foxglove Penstemon can be distinguished from other members of the genus by the absence of hairs on the leaves and stems, a corolla that is primarily white on the outer surface (but sometimes with violet tints), the presence of tiny white hairs on the anthers (resembling small combs), and an absence of ridges on the lower inner surface of the corolla. The small hairs on the anthers can lodge against the hairs of a visiting bee, causing the stamens to bend downward to deposit pollen on the back of the insect, if it is sufficiently large in size.