Monogr. Acad. Nat. Sci. Philadelphia 1: 212. 1935.
Herbs. Stems ascending to erect, 40–90 cm, retrorsely hairy proximally, usually retrorsely hairy distally, not glaucous. Leaves basal and cauline, basal sometimes withering by anthesis, not leathery, glabrate to puberulent; basal and proximal cauline 40–150 × 10–26 mm, blade oval to elliptic, base tapered, margins entire or ± denticulate, apex rounded to obtuse; cauline 7 or 8 pairs, sessile, 17–110 × 3–20 mm, blade oblanceolate to lanceolate, base tapered to clasping, margins entire or denticulate to serrulate, apex obtuse to acute. Thyrses interrupted, conic, 11–22 cm, axis glabrous or sparsely glandular-pubescent, verticillasters 4–6, cymes (2–)5–8-flowered, 2 per node; proximal bracts lanceolate, 10–15 × 3–5 mm, margins entire; peduncles and pedicels ascending to erect, glabrous or sparsely glandular-pubescent. Flowers: calyx lobes ovate, 1.5–3.5(–4) × 0.9–1.5 mm, sparsely glandular-pubescent; corolla white, sometimes tinged lavender or purple, with reddish purple nectar guides, ventricose, 15–20(–22) mm, glandular-pubescent externally, sparsely white-pubescent internally abaxially, tube 5–6 mm, throat abruptly inflated, 5–7 mm diam., slightly 2-ridged abaxially; stamens included, pollen sacs opposite, navicular, 0.8–1 mm, dehiscing completely, connective splitting, sides glabrous, sometimes sparsely pubescent, hairs white, to 0.2 mm, sutures papillate; staminode 8–10 mm, reaching orifice, 0.3–0.4 mm diam., tip straight to slightly recurved, distal 3–4 mm pilose, hairs yellowish, to 1 mm; style 10–12 mm. Capsules 5–8 × 4–5 mm, glabrous.
Phenology: Flowering May–Jun.
Habitat: Rocky oak woods, fields.
Elevation: 100–200 m.
A. C. Koelling (1964) assessed Penstemon deamii and its allies using morphological, cytological, and breeding studies. He concluded that P. deamii is a distinct member of the eastern North American polyploids that include P. calycosus, P. digitalis, and P. laevigatus. Geographically sympatric with P. calycosus and P. digitalis, P. deamii is distinguished from those two species by its shorter calyx lobes [1.5–3.5(–4) mm versus 4–9 mm], corollas [15–20(–22) mm versus (17–)20–35 mm], and pollen sacs (0.8–1 mm versus 1.2–1.7 mm). The species appears to be limited to Clark, Crawford, Floyd, Harrison, and Marion counties (K. Yatskievych 2000). Reports of P. deamii from southern Illinois appear to be based on specimens of questionable provenance or misidentifications (Koelling).