Amer. Midl. Naturalist 23: 595. 1940.
Subshrubs. Stems ascending to erect, 10–40 cm, moderately to densely retrorsely hairy, not glaucous. Leaves basal and cauline, opposite, rarely alternate, not leathery, ± retrorsely hairy; basal and proximal cauline 10–25(–65) × 1–2(–6) mm, blade linear, base tapered, margins entire, apex acute, rarely obtuse; cauline 7–10 pairs, sessile or proximals sometimes petiolate, 4–45 × 1–4(–6) mm, blade linear, rarely lanceolate distally, base truncate or clasping, margins entire, usually revolute, apex acute. Thyrses interrupted, cylindric, 3–18 cm, axis retrorsely hairy and glandular-pubescent, sometimes only retrorsely hairy, verticillasters 3–7, cymes 1- or 2(or 3)-flowered, 2 per node; proximal bracts lanceolate to linear, 5–24 × 1–2 mm, margins entire; peduncles and pedicels ascending to erect, retrorsely hairy and glandular-pubescent. Flowers: calyx lobes broadly lanceolate, 4–6.5 × 1.5–3 mm, glandular-pubescent; corolla blue to violet or purple, with violet nectar guides, funnelform, (13–)15–22 mm, glandular-pubescent externally, glabrous internally, tube 5–6 mm, throat gradually inflated, 4–6(–7) mm diam., slightly 2-ridged abaxially; stamens included, pollen sacs opposite, navicular, 1.1–1.3 mm, dehiscing completely, connective splitting, sides glabrous, sutures papillate; staminode 13–17 mm, exserted, 0.5–0.9 mm diam., tip straight, distal 7–9 mm sparsely yellow-pubescent, hairs to 1 mm; style 11–13 mm. Capsules 6–8 × 3–5 mm, glabrous.
Phenology: Flowering Jun–Jul.
Habitat: Sagebrush shrublands, juniper woodlands.
Elevation: 1000–2100 m.
Penstemon seorsus is known from the southern Columbia Plateau and northwestern Great Basin. The species has been documented in Adams, Owyhee, and Washington counties, Idaho, and in Baker, Grant, Harney, Jefferson, Malheur, and Wasco counties, Oregon.