Large-Flowered Penstemon
Penstemon grandiflorus
Snapdragon family (Scrophulariaceae)

Description: This is a short-lived perennial plant that forms a basal rosette during its first year, after which it produces one or more flowering stalks about 1-3' tall from a thick rootstock. The basal leaves (2-5" long and 1-3" across) are pale grayish green or bluish green, ovate to obovate in shape, smooth along their margins, and glabrous, tapering either gradually or abruptly into petioles. They have a rather succulent texture. The stems of flowering plants are whitish green to pale red, terete (circular in cross-section), glabrous, and somewhat glaucous. The leaves along these stems are arranged oppositely; they are 2-4" in length and 1-2" across. These latter leaves are pale grayish green to bluish green, ovate to ovate-cordate in shape, smooth along their margins, and glabrous; their tips are blunt. The leaves of each lower stem are sessile, while the smaller upper leaves often clasp the stem. Like the basal leaves, the opposite leaves have a rather succulent texture. From the axils of opposite leafy bracts (up to 1" long and " across), there develops pairs of 1-3 flowers on short slender pedicels, forming a narrow raceme about -1' long.  Each flower has a pinkish lavender corolla up to 2" long, a pale grayish green or bluish green calyx with 5 teeth, a pistil with a single white style, and 5 stamens. The corolla is tubular-trumpet shaped and slightly flattened; it has an upper lip with two rounded lobes and a lower lip with 3 rounded lobes. Within the throat of the corolla, there are fine purple veins that function as nectar guides. Along the upper outer surface of the corolla, there is a slender longitudinal ridge. The glabrous calyx is less than " in length; its teeth are lanceolate. The tip of the white style, where the stigma occurs, is slightly swollen. The leafy bracts of the flowers are similar in appearance to the opposite leaves, except they are smaller in size. Similar to the upper leaves, their bases clasp the stem. The blooming period occurs from late spring to early summer, lasting about 3 weeks. Each flower remains in bloom for only a short time. There is no floral scent. The flowers are replaced by ovoid seed capsules that are a little longer than the toothed calyx. Each capsule contains numerous small seeds. The seeds are distributed to a limited extent by the wind when the stems of flowering plants sway back and forth. The root system consists of a stout taproot with coarse secondary roots. This taproot extends deep into the soil.

Cultivation: The preference is full sun, dry conditions, and poor soil containing rocky material or sand. This plant is easy to grow in locations that are sunny and well-drained, but it is rather short-lived. However, its seeds are fairly easy to germinate. Foliar disease is rarely troublesome; the biggest threat is root rot from poorly drained soil. Sometimes spider mites can be found on the foliage, but they appear to cause little damage. This plant has excellent drought resistance.

Range & Habitat: The native Large-Flowered Penstemon occurs in only a few northern or NW counties in Illinois (see Distribution Map), where it is rare and state-listed as 'endangered.' This plant is more common in states that are located to the west of the Mississippi River. Habitats include dry sand prairies, dolomite prairies, and gravelly hill prairies. Because of the showy flowers, Large-Flowered Penstemon is more often found in flower gardens, from where it rarely escapes. Fire is supposed to be harmful to the ecological success of this plant because its growing buds remain above ground. In its natural habitat, significant wildfires rarely occur because of the sparse vegetative cover.

Faunal Associations: The flowers are cross-pollinated by bumblebees and other long-tongued bees, including Osmia distincta and Synhalonia dubitata. These latter two bees appear to prefer the flowers of Penstemon spp. over other species. One long-tongued bee, Xylocopa virginica (Large Carpenter Bee), perforates the base of the corolla from the outside to rob nectar from Large-Flowered Penstemon. An unusual wasp, Pseudomaris occidentalis, is a specialist pollinator (oligolege) of Penstemon spp. Like many bees, this wasp uses nectar and pollen to feed its larvae. While the more western range of this wasp overlaps with the range of Large-Flowered Penstemon, it has not been observed in Illinois. Other floral visitors include pollen-seeking Halictid bees, masked bees (Hylaeus spp.), and Syrphid flies. Insects that feed destructively on the foliage and other parts of Penstemon spp. are uncommon, but they include the caterpillars of a moth, Elaphria chalcedonia (Chalcedony Midget), and Spharagemon collare (Mottled Sand Grasshopper). At the present time, information about the relationships between Large-Flowered Penstemon and vertebrate animals is unavailable.

Photographic Location: The photographs were taken at the webmaster's wildflower garden in Urbana, Illinois. The plants are an Illinois ecotype of this species from nursery-grown material.

Comments: Both the foliage and flowers of Large-Flowered Penstemon are beautiful and distinctive. Unfortunately, the blooming period of the flowers is rather short, but you can't have everything. Because of its distinctive bluish foliage and large flowers (up to 2" in length), this species is easy to distinguish from other Penstemon spp. that are native to Illinois. However, a non-native species from the west, Penstemon cobaea (Showy Penstemon), is somewhat similar in appearance and its flowers are equally large in size. Unlike Large-Flowered Penstemon, this latter species has pubescent stems, while its upper leaves and bracts have bases that are sessile, rather than clasping. Showy Penstemon has naturalized in Kane County, Illinois.

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