Penstemon is the largest genus of flowering plants endemic to North America, with over 270 species. Penstemon strictus — Rocky Mountain Penstemon or Blue Penstemon — is one of the most common and showiest, producing dense spikes of intense blue-violet tubular flowers through early summer. For botanical illustrators, it offers an excellent subject for learning to draw bilabiate (two-lipped) flowers, which appear across many plant families.

Key Structural Features

The flowers are borne in a narrow, somewhat one-sided spike at the top of a stiff, upright stem that reaches 30-70 cm. Each flower is tubular, about 2.5-3 cm long, with a two-lipped mouth: the upper lip has two lobes, the lower lip has three. The corolla expands gradually from a narrow base to a wider opening, creating a funnel shape when viewed from the side.

The defining feature of the genus is the staminode — a sterile fifth stamen that does not produce pollen. In Penstemon strictus, the staminode is bearded (covered in hairs), which is the origin of the common name "beardtongue." The staminode extends along the lower lip of the corolla and is visible at the flower's mouth. Illustrating the staminode clearly, ideally with a magnified dissection view, is essential for a complete Penstemon illustration.

The leaves are opposite, lance-shaped, and smooth-edged. The basal leaves are broader and petiolate (stalked), while the upper stem leaves are narrower and sessile (clasping the stem directly). This leaf variation along the stem is an important detail to capture.

Drawing Challenges

The corolla interior. The flowers face outward and slightly downward, meaning you're often looking into the opening. Drawing the interior of a tubular flower convincingly — showing the upper and lower lip separation, the four fertile stamens pressed against the upper corolla wall, and the hairy staminode along the floor — requires careful observation and confident mark-making. A dissected flower (cut lengthwise) is the clearest way to show these internal structures.

The spike architecture. Flowers are arranged in whorls (clusters) at nodes along the spike, with each whorl slightly separated from the next. The overall effect is architectural — almost geometric. Getting the spacing between whorls right, and showing how the flowers in each whorl radiate outward, gives the illustration a sense of the plant's growth habit.

Color. P. strictus flowers are a rich blue-violet that can be difficult to capture in watercolor. The color often appears more blue in bright light and more violet in shade. If working in pen and ink, the tonal value of the corolla is medium-dark — dense enough to read as a saturated color, but not so dark that interior details are lost.

Recommended Approach

Include the full flowering spike to show the overall inflorescence structure, plus at least one individual flower shown from the side (to reveal the funnel shape) and from the front (to show the two-lipped opening). A longitudinal dissection showing the staminode, fertile stamens, and pistil completes the botanical plate.

Penstemon species are abundant in the Rocky Mountain region from May through July. Set your Botanical Gesture Lab location to any Colorado mountain area during this period for rich iNaturalist results. The genus is so diverse that once you've drawn one species, you'll find subtle but meaningful differences in flower size, color, leaf shape, and staminode hair pattern across different species — each one worth its own illustration.