Bull. Torrey Bot. Club 25: 280. 1898. (as Pentstemon)
Herbs. Stems ascending to erect, (15–)20–42 cm, retrorsely hairy or puberulent, not glaucous. Leaves essentially cauline, basal absent or poorly developed, not leathery, ± puberulent; cauline (4 or)5–8 pairs, sessile, (20–)30–65 × (2–)4–10(–20) mm, blade ovate to lanceolate, base tapered, margins entire, apex obtuse to acute. Thyrses interrupted or continuous, cylindric, 5–14 cm, axis glandular-pubescent, verticillasters (2 or)3–6, cymes 2–4(–8)-flowered, 2 per node; proximal bracts lanceolate to linear, 7–46 × 1–10(–20) mm, margins entire; peduncles and pedicels ascending to erect, glandular-pubescent. Flowers: calyx lobes lanceolate, 5–8 × 1.2–2.5 mm, glandular-pubescent; corolla blue to dark blue, purple, or violet, with reddish purple nectar guides, bilabiate, not personate, funnelform, 16–23 mm, glandular-pubescent externally, moderately yellowish lanate internally abaxially, tube 4.5–6 mm, throat slightly inflated, 4–6 mm diam., 2-ridged abaxially; stamens included, pollen sacs opposite, navicular to subexplanate, 0.8–1.3 mm, dehiscing completely, connective splitting, sides glabrous, sutures papillate; staminode 10–12 mm, included, 0.3–0.4 mm diam., tip straight, distal 1 mm densely pilose or lanate, hairs yellow, to 1.4 mm, remaining distal 4–5 mm sparsely pilose, hairs yellow, to 0.5 mm; style 11–14 mm. Capsules 5–8 × 3.5–5 mm, glabrous. 2n = 16.
Phenology: Flowering May–Jul.
Habitat: Rocky flats, slopes, ravines, sagebrush shrublands, pine woodlands.
Elevation: 1500–2400 m.
Colo., Idaho, Mont., Nev., Utah, Wyo.
Penstemon radicosus is known from the Central Rocky Mountains and mountain ranges in the northern Great Basin. The species is most likely to be confused with P. laxus or P. watsonii.