Penstemon cobaea var. purpureus

Species Native to Missouri
Common Name: dew flower 
Type: Herbaceous perennial
Family: Plantaginaceae
Native Range: Central United States
Zone: 5 to 8
Height: 1.00 to 3.00 feet
Spread: 1.00 to 1.50 feet
Bloom Time: May
Bloom Description: Purple
Sun: Full sun
Water: Dry to medium
Maintenance: Low
Flower: Showy
Tolerate: Deer, Drought, Dry Soil, Shallow-Rocky Soil


Easily grown in average, dry to medium, well-drained soils in full sun. Prefers somewhat dry, calcareous soils. Avoid wet, poorly-drained soils.

Noteworthy Characteristics

Penstemon cobaea, commonly called purple beardtongue, prairie beardtongue, or cobaea beardtongue, is a clump-forming, herbaceous perennial which occurs on prairies, limestone glades and rocky bluffs in the Great Plains and the Ozark Plateau regions of the south-central United States (including Missouri). Mature plants will typically grow 1-2.5' tall. Features showy, loose, terminal panicles of white to violet to deep purple, 2" long, tubular flowers atop erect, rigid, downy stems. Flowers bloom in mid-spring and are somewhat larger than most penstemons. The leaves are primarily clasping, lanceolate to elliptic in shape, and will reach up to roughly 4.75" long and 2" wide.

Var. purpureus has uniformly purple flowers whereas the species, Penstemon cobaea, has white to pale lilac flowers. The native range of var. purpureus centers on the Ozark Plateau where it occurs only on certain limestone glades.

The genus name Penstemon likely comes from the Latin paene meaning "almost" or "nearly" and the Greek stemon meaning "stamen". The name may also comes from the Greek penta meaning "five" and stemon meaning "stamen". Both refer to the fifth, sterile stamen (staminode) that characterizes members of this genus.

The common names of this species refer to the color of the blooms or its native habitat. Dew flower may refer the appearance of the glandular hairs covering the stem and emerging flower buds. Penstemons are sometimes commonly called beardtongues because the sterile stamen (staminode) can be hairy.


No serious insect or disease problems. Root rot can occur in wet, poorly-drained soils.


A rare plant for limestone rock gardens, native plant gardens or borders.