Herbs. Stems ascending or erect, 8–40(–60) cm, glabrate, retrorsely hairy, or glandular-pubescent, not glaucous. Leaves basal and cauline, not leathery, retrorsely hairy or pubescent, sometimes also glandular-pubescent; basal and proximal cauline 25–100(–150) × (4–)9–20(–34) mm, blade elliptic to ovate, base tapered, margins ± serrate to dentate, apex obtuse to acute; cauline 2–5 pairs, sessile, 11–60 × 5–25(–30) mm, blade triangular-ovate to lanceolate, base truncate to cordate-clasping, margins serrate to dentate, apex acute, rarely obtuse. Thyrses interrupted, cylindric, 4–28 cm, axis densely glandular-pubescent, rarely sparsely glandular-pubescent, verticillasters 3–8, cymes 3–11-flowered, 2 per node; proximal bracts ovate to lanceolate, 8–58 × 4–25 mm, margins serrate, sometimes entire; peduncles and pedicels ascending to erect, densely glandular-pubescent. Flowers: calyx lobes ovate to lanceolate, 2.5–4.5(–6) × 0.9–1.5 mm, glandular-pubescent; corolla blue to lavender, purple, or violet, with purple nectar guides, funnelform, 11–16 mm, glandular-pubescent externally, sparsely white-villous internally abaxially, tube 4–5 mm, throat gradually inflated, 3–6 mm diam., rounded abaxially; stamens included or longer pair reaching orifice, pollen sacs opposite, navicular to subexplanate, 0.6–0.8 mm, dehiscing completely, connective splitting, sides glabrous, sutures smooth; staminode 7–9 mm, included or slightly exserted, 0.2–0.3 mm diam., tip recurved, distal 0.5–1 mm densely pilose, hairs yellow, to 0.8 mm; style 8–10 mm. Capsules 4–7 × 3–4 mm, glabrous. 2n = 16.
Phenology: Flowering Apr–Jul.
Habitat: Open grassy, sandy, gravelly, and rocky slopes, pine and pine-fir woodlands, sagebrush shrublands.
Elevation: 300–2000 m.
Penstemon pruinosus occurs along the eastern slope of the Cascade Range in Chelan, Douglas, Grant, and Kittitas counties, Washington, east into the scablands of Adams and Franklin counties, Washington, and north into extreme southern British Columbia.
A blue dye is made from the flowers of Penstemon pruinosus by the Okanagan-Coville tribe of northeastern Washington (D. E. Moerman 1998).