Monogr. Acad. Nat. Sci. Philadelphia 1: 229. 1935.
Herbs. Stems ascending to erect, 25–65(–70) cm, puberulent or retrorsely hairy, rarely also glandular-pubescent distally, not glaucous. Leaves basal and cauline, basal often withering by anthesis, not leathery, glabrous or retrorsely hairy to puberulent; basal and proximal cauline 25–90 × 8–25 mm, blade spatulate, oblanceolate, or ovate, base tapered, rarely truncate, margins subentire or serrate to dentate, apex rounded to obtuse or acute; cauline (3–)5–7 pairs, short-petiolate or sessile, (20–)30–90(–110) × (2–)5–22 mm, blade lanceolate to oblanceolate, base tapered to cordate-clasping, margins subentire or serrate to dentate, apex acute. Thyrses interrupted, conic, 5–26(–32) cm, axis retrorsely hairy and ± glandular-pubescent, verticillasters 3–7, cymes 2–6-flowered, branches of each cyme usually elongating, of equal length, 2 per node; proximal bracts lanceolate, 4–28 × 1–6 mm, margins entire or ± serrulate; peduncles and pedicels spreading or ascending, puberulent or retrorsely hairy and, usually, glandular-pubescent. Flowers: calyx lobes ovate to lanceolate, 2.5–5.5 × 2–3 mm, sparsely puberulent and glandular-pubescent; corolla white to light lavender, sometimes tinged pink, with reddish purple nectar guides, tubular, 20–28(–30) mm, glandular-pubescent externally, moderately white- or yellow-lanate internally abaxially, tube 5–7 mm, throat abruptly inflated, 4–8 mm diam., 2-ridged abaxially; stamens included, pollen sacs opposite, navicular, 1–1.3 mm, dehiscing completely, connective splitting, sides glabrous, sutures papillate; staminode 15–20 mm, exserted, 0.6–0.8 mm diam., tip straight to slightly recurved, distal 8–10 mm densely pilose, hairs yellow, to 1.5 mm; style 14–20 mm. Capsules 8–10 × 6–7 mm, glabrous. 2n = 16.
Phenology: Flowering Mar–Jun.
Habitat: Sandy or rocky open woods, tallgrass prairies, sand barrens.
Elevation: 10–500 m.
Ala., Ark., La., Miss., Okla., Tex.
Penstemon laxiflorus is a species of the central and western Gulf Coastal Plain and southern Interior Lowland. Pennell cited one specimen each from Florida and Georgia; specimens from those states have not been confirmed. The species shares many features with P. australis, which occurs farther east along the southern Atlantic Coastal Plain and eastern Gulf Coastal Plain. Penstemon laxiflorus usually can be distinguished from P. australis by stem vestiture. Penstemon laxiflorus has stems with only short, retrorse hairs or, if glandular hairs also are present, they are sparse and occur just below the inflorescences. By contrast, P. australis has stems with a distinct mix of short, eglandular hairs and much longer, glandular hairs.