Herbs. Stems erect, 30–86 cm, retrorsely hairy and glandular-lanate, not glaucous. Leaves basal and cauline, not leathery, retrorsely hairy, sometimes also glandular-pubescent, rarely glabrate; basal and proximal cauline 32–130 × 7–40 mm, blade spatulate to oblanceolate, base tapered, margins entire or ± serrate, apex rounded to obtuse; cauline 5–8 pairs, sessile or proximals short-petiolate, 16–122 × 3–23 mm, blade lanceolate, base clasping or tapered, margins ± serrate, apex acute to acuminate. Thyrses interrupted, narrowly conic, rarely conic, 7–26 cm, axis ± glandular-pubescent, verticillasters 3–6, cymes 2–6-flowered, usually only 1 branch of each cyme elongating, others nearly sessile or distinctly shorter, 2 per node; proximal bracts lanceolate, 3–20 × 1–4 mm, margins entire; peduncles and pedicels erect, sometimes ascending, ± glandular-pubescent. Flowers: calyx lobes ovate to lanceolate, 4–5.2 × 1.6–2.3 mm, sparsely glandular-pubescent; corolla white to pinkish or light lavender, with dark purple nectar guides, tubular, 20–25 mm, glandular-pubescent externally, moderately white-lanate internally abaxially, tube 4–5 mm, throat abruptly inflated, 4.5–6 mm diam., 2-ridged abaxially; stamens included, pollen sacs opposite, navicular, 1.2–1.5 mm, dehiscing completely, connective splitting, sides glabrous, sutures papillate; staminode 11–14 mm, exserted, 0.4–0.7 mm diam., tip straight to slightly recurved, distal 8–10 mm densely pilose, hairs yellow, to 2 mm; style 10–12 mm. Capsules 6–9 × 4.5–6 mm, glabrous.
Phenology: Flowering Mar–Jun.
Habitat: Sandy pine and oak woodlands, pine savannas, hammocks, granite hills, sandy open areas.
Elevation: 10–200 m.
Ala., Fla., Ga., Miss., N.C., S.C., Tenn., Va.
Penstemon australis is known from the southern Atlantic Coastal Plain and eastern Gulf Coastal Plain. The species is confused most often with P. laxiflorus, which occurs farther west. Penstemon australis is distinguished from P. laxiflorus most readily by the stem vestiture; P. australis usually has stems with a mix of short, eglandular hairs and much longer, glandular hairs, while P. laxiflorus has stems with only short, retrorse hairs or, if glandular hairs also are present, they are sparse and occur just below the inflorescences. Penstemon australis also tends to have narrower inflorescences due to the unequal elongation of cyme branches. Ranges of the two species overlap in southwestern Alabama, and many specimens from Baldwin, Escambia, and Mobile counties are morphologically intermediate.
Many specimens of Penstemon from the Appalachian Piedmont, especially in northeastern Alabama, northern Georgia, central North Carolina, and western South Carolina, combine morphological features of P. australis and P. canescens. These plants usually have equally developed cyme branches (as in P. canescens) but ascending or erect peduncles and pedicels (as in P. australis). Leaf shape generally is intermediate between P. australis and P. canescens. F. W. Pennell in the 1930s annotated most such specimens as P. australis. F. S. Crosswhite (1965e) also included these specimens in his concept of P. australis, assigning them subspecies status, though he never published the subspecies names that he used in his thesis and on herbarium sheets. The relationship of these plants remains unclear; they will key to P. canescens or P. laxiflorus.
A. E. Radford et al. (1968) gave a chromosome number of n = 8 for Penstemon australis; this does not appear to be supported by any other published chromosome count.