Mem. New York Bot. Gard. 1: 348. 1900. (as Pentstemon)
Herbs. Stems ascending to erect, 6–20(–25) cm, retrorsely hairy proximally, glabrous or retrorsely hairy distally, not glaucous. Leaves basal and cauline, not leathery, glabrous or ± puberulent; basal and proximal cauline 15–65 × 1–5(–7) mm, blade narrowly oblanceolate to linear, base tapered, margins entire, apex obtuse to acute; cauline 2–5 pairs, short-petiolate or sessile, 7–33 × 1–3 mm, blade lanceolate to linear, base sessile to clasping, margins entire, apex obtuse to acute. Thyrses interrupted, cylindric, 2–11 cm, axis glandular-pubescent, sometimes also retrorsely hairy, verticillasters 2–6, cymes 1–5-flowered, 2 per node; proximal bracts lanceolate to linear, 9–32 × 1–6 mm, margins entire; peduncles and pedicels erect, ± glandular-pubescent. Flowers: calyx lobes ovate to lanceolate, 2.2–4.6 × 1–2.4 mm, glandular-pubescent; corolla blue to violet, with reddish purple guides, funnelform, 11–17 mm, glandular-pubescent externally, moderately whitish lanate internally abaxially, tube 3–4 mm, throat gradually inflated, 4–6 mm diam., 2-ridged abaxially; stamens included, pollen sacs divergent to opposite, subexplanate to explanate, 0.6–0.8 mm, dehiscing completely, connective splitting, sides glabrous, sutures papillate; staminode 7–8 mm, reaching orifice, 0.2–0.4 mm diam., tip recurved, distal 0.5–1 mm densely pilose, hairs golden yellow, to 0.8 mm; style 9–10 mm. Capsules 5–7 × 4–5 mm, glabrous.
Phenology: Flowering Jun–Jul.
Habitat: Rocky hillsides, sagebrush shrublands, montane grasslands.
Elevation: 1500–2900 m.
Idaho, Mont., Wyo.
Penstemon aridus is known from the Rocky Mountains in eastern Idaho and southwestern and south-central Montana and the Big Horn and northern Absaroka Mountains of Wyoming. The sometimes grasslike basal leaves distinguish P. aridus from P. humilis and P. virens. At lower elevations or in shaded, forest habitats, plants sometimes have broader basal leaves and tend to be much taller than typical plants; the broadly scarious-margined calyx lobes of P. aridus distinguish it from similar species.