Penstemon arkansanus Pennell

Growth Form

Penstemon arkansanus Pennell is a perennial herb that grows in clustered stems reaching 30 to 60 cm (12 to 24 inches) in height.

Stem Characteristics

Its stems are greyish and covered in fine short hairs, and they often turn purplish.

Leaf Characteristics

The leaves are also covered in fine short hairs, with the longest leaves reaching 7 to 10 cm (2.8 to 3.9 inches) long.

Inflorescence Structure

A flowering thyrse makes up just under half of the plant's total height, and this thyrse holds 3 to 9 fascicles, each made up of two axillary branches.

Flower Stalk Dimensions

The individual flower stalks, pedicels, are shorter than the main stalk, peduncle, of each fascicle.

Sepal Size

The sepals are 2 to 3 mm (0.079 to 0.118 inches) long when the plant is flowering (anthesis), and grow to 4 to 5 mm (0.16 to 0.20 inches) long when the plant develops fruit.

Corolla Appearance

The corolla is white, 15 to 17 mm (0.59 to 0.67 inches) long, and has purplish veins on its inner anterior side.

Corolla Tube Size

The corolla tube and narrow throat are 11 to 12 mm (0.43 to 0.47 inches) long.

Seed Capsule Traits

The smooth, hairless (glabrous) seed capsule is 6 to 7 mm (0.24 to 0.28 inches) long and remains hidden when fully mature.

Species Distinction

This species only differs from Penstemon pallidus in that it tends to be more hairless (glabrous) overall.

Flowering Period

Penstemon arkansanus flowers from late May into early June.