Contr. U.S. Natl. Herb. 16: 171. 1913.
Stems ascending to erect, 32–100 cm, glabrous, slightly glaucous. Leaves glabrous, not glaucous; basal and proximal cauline 40–80 (–150) × 14–40 (–60) mm, blade spatulate to obovate, oblanceolate, or elliptic, base tapered, margins entire, apex rounded to obtuse; cauline 3–7 pairs, sessile, (11–) 20–135 × 9–50 mm, blade spatulate to elliptic, ovate, or subcordate, base truncate to broadly cordate-clasping, apex rounded to acute or mucronate. Thyrses secund, (3–) 6–44 cm, axis glabrous, verticillasters 3–15, cymes 2–4 (–8) -flowered; proximal bracts suborbiculate, ovate, or lanceolate, (4–) 16–60 × (2–) 5–45 mm; peduncles and pedicels erect, glabrous. Flowers: calyx lobes ovate, 1.6–6 × 1.4–3 mm, margins entire or erose, glabrous; corolla red to crimson, with reddish violet nectar guides, bilaterally symmetric, weakly bilabiate, tubular, 22–30 mm, densely yellow-villous internally abaxially, tube 6–8 mm, throat 6–8 mm diam., constricted at orifice, rounded abaxially, abaxial lobes spreading to reflexed, adaxial lobes projecting to erect; stamens included, pollen-sacs divergent, 1.5–1.9 mm, sides glabrous, sutures denticulate, teeth to 0.1 mm; staminode 15–17 mm, included or slightly exserted, tip straight to recurved, distal 1–3 mm sparsely lanate, hairs yellow, to 1.5 mm; style 18–28 mm, usually exserted. Capsules 10–15 × 5–9 mm.
Varieties 2 (2 in the flora).
Penstemon cardinalis occurs as two weakly differentiated varieties in isolated ranges of the Southern Rocky Mountains.
|1||Calyx lobes 1.6–3.5(–4) × 1.4–2 mm; cauline leaf blades elliptic to spatulate or ovate, not leathery; proximal bracts ovate to lanceolate.||Penstemon cardinalis var. cardinalis|
|1||Calyx lobes 4–6 × 2.3–3 mm; cauline leaf blades ovate to subcordate, sometimes elliptic, leathery; proximal bracts suborbiculate to ovate.||Penstemon cardinalis var. regalis|
"/4+timescorollathroat" is not declared as a valid unit of measurement for this property.