Brittonia 39: 412, fig. 1. 1987.
Caudex herbaceous, rhizomelike. Stems ascending, 4–9 cm, puberulent to glandular-pubescent, sometimes glabrate proximally, not glaucous. Leaves cauline, leathery, glabrous, glaucous; cauline 1 or 2, sessile or short-petiolate, 7–28(–32) × 3–12 mm, blade obovate to oblanceolate or elliptic, base tapered, with a white band 0.2 mm wide, apex rounded to obtuse or acute. Thyrses continuous, ± secund, 1–7 cm, axis puberulent to glandular-pubescent, verticillasters 2–6, cymes 1- or 2(or 3)-flowered, 2 per node; proximal bracts obovate to oblanceolate, 14–32 × 8–14 mm; peduncles and pedicels puberulent to glandular-pubescent. Flowers: calyx lobes lanceolate, 5.5–7 × 1.5–2.2 mm, glabrous; corolla white to lavender, without nectar guides, funnelform to weakly ventricose, (14–)17–20 mm, glabrous externally, glabrous internally, tube 6–7 mm, throat gradually inflated, not constricted at orifice, 6–8 mm diam., slightly 2-ridged abaxially; stamens included, pollen sacs divergent, navicular, 0.9–1.4 mm, dehiscing incompletely, proximal 1/5–1/4 indehiscent, connective not splitting, sides sparsely hispid, hairs white, to 0.4 mm, sutures denticulate, teeth to 0.1 mm; staminode 9–10 mm, included or slightly exserted, 0.5–0.6 mm diam., tip straight, 7–9 mm sparsely pilose, hairs yellow, to 1 mm; style 9–11 mm. Capsules 3.5–7.5 × 2.5–5 mm.
Phenology: Flowering Jun–Jul.
Habitat: Oil-shale talus slopes.
Elevation: 2400–2700 m.
Penstemon debilis is known from the vicinity of Mt. Callahan, Mt. Logan, and the Roan Plateau in Garfield County. Plants grow on steep, sparsely vegetated oil-shale talus slopes of the Parachute Creek Member of the Green River Formation (S. L. O’Kane 1988; S. Spackman et al. 1997).
McMullen, A. L. 1998. Factors Concerning the Conservation of a Rare Shale Endemic Plant: The Reproductive Ecology and Edaphic Characteristics of Penstemon debilis (Scrophulariaceae). M.S. thesis. Utah State University.