Herbs. Stems ascending to erect, (18–)30–80 cm, puberulent or retrorsely hairy proximally, puberulent or glandular-pubescent distally, not glaucous. Leaves deciduous, 8–13 pairs, short-petiolate or sessile, 23–130 × 3–20 mm, blade lanceolate, rarely linear, base tapered, margins entire or remotely serrate, apex acute to acuminate, rarely obtuse, glabrous or puberulent to pubescent, not glaucous. Thyrses interrupted, ± secund, (3–)6–15(–28) cm, axis sparsely to moderately glandular-pubescent, verticillasters 3–7, cymes 2–7-flowered; proximal bracts lanceolate to linear, (5–)15–80 × (1–)2–8(–20) mm; peduncles and pedicels spreading or ascending, glandular-pubescent. Flowers: calyx lobes lanceolate, 7–16 × 2–4 mm, glandular-pubescent; corolla lavender to purple, unlined internally or lined with faint lavender nectar guides abaxially, nearly personate, funnelform, 35–46 mm, glabrous externally, moderately white-lanate internally abaxially, tube 8–14 mm, throat 8–12 mm diam.; stamens included, pollen sacs 1.1–1.8 mm; staminode 10–13 mm, flattened distally, 0.2–0.3 mm diam., tip straight, glabrous; style 30–40 mm. Capsules 10–14 × 5–7 mm.
Phenology: Flowering Jun–Aug.
Habitat: Rocky slopes, rock outcrops, gravel bars along streams.
Elevation: 600–2400 m.
Alta., B.C., Idaho, Mont., Wash.
Penstemon lyallii is known from the Central, Northern, and Canadian Rocky mountains in southwestern Alberta, southeastern British Columbia, northern Idaho, northwestern Montana, and northeastern Washington.