1. Penstemon arkansanus Pennell (Arkansas beard-tongue)

Pl. 484 j–l; Map 2213

Stems 25–60 cm long, erect or ascending, densely pubescent with minute, nonglandular hairs, sometimes also with slightly longer glandular hairs toward the tip, occasionally glabrous or nearly so toward the base, olive green to grayish green or more commonly purplish-tinged, not glaucous. Basal leaves 2–6(–9) cm long, the blade oblanceolate to spatulate or obovate, rounded to bluntly pointed at the tip, tapered basally to a usually winged petiole, the margins bluntly to sharply and usually finely toothed, the surfaces glabrous to more commonly sparsely to moderately nonglandular-hairy, mostly along the margins and main veins, not glaucous. Stem leaves 2–8(–10) cm long, the lowermost with the blade oblanceolate to narrowly oblong-elliptic, grading into lanceolate or narrowly lanceolate at the stem tip, rounded to sharply pointed at the tip, sessile or nearly so, the base of the lower blades tapered, grading through rounded to those of the uppermost leaves sometimes shallowly cordate and clasping, the margins variously bluntly to sharply and sometimes minutely toothed, at least above the midpoint, the surfaces sparsely to densely and minutely nonglandular-hairy, sometimes only along the main veins, occasionally also dotted with widely spaced, sessile glands, not glaucous. Inflorescences narrow to occasionally more broadly pyramidal panicles, the central axis minutely glandular-hairy, green or purplish-tinged, not glaucous, with (2–)3–7(–9) nodes, each with a pair of relatively small, linear to narrowly lanceolate, somewhat clasping bracts, the branches ascending or arched upward, with a pair of few- to several-branched clusters per node, each main branch with 3–9(–13) flowers. Calyces 2–4 mm long at flowering, moderately to densely glandular-hairy, not glaucous, the lobes ovate. Corollas 15–18 mm long, the tube abruptly but relatively slightly enlarged below the midpoint (usually very slightly so on the lower side), strongly bilabiate, the upper lip spreading to somewhat recurved, the lower lip spreading to somewhat reflexed, white or occasionally pale pinkish- to purplish-tinged, the throat appearing slightly flattened, relatively strongly 2-ridged and usually lined with purple nectar guides on the lower side, minutely glandular-hairy externally and sparsely so in the throat. Staminode white, strongly flattened toward the tip, bearded on the upper surface, the hairs yellow or purple toward the base, slightly curved downward apically and bearded with yellow hairs. Fruits 5–7 mm long. Seeds 0.7–1.0 mm long, dark brown to black, the reddish brown ridges poorly developed. 2n=16. April–June.

Uncommon in the southwestern portion of the Ozark Division eastward to Howell County; also disjunct in Cape Girardeau County (Texas, Oklahoma, Missouri, Arkansas, and Illinois). Glades, ledges and tops of bluffs, savannas, openings of dry upland forests, and banks of streams; also roadsides; usually on calcareous substrates.

Gleason and Cronquist (1991) and some other authors have treated P. arkansanum as a small-flowered form of P. pallidum. Steyermark (1963) and McWilliam (1967) presented strong morphological evidence for keeping these two species separate. Koelling (1964) did not fully treat the taxon, but mentioned that he considered it a distinct species. Both are apparently diploids and thus might possibly have been involved in the parentage of such polyploids as P. digitalis. Pending more detailed taxonomic studies, it has been accepted as distinct in the present treatment. Interestingly, specimens and photographs attributed to P. arkansanus are more frequently misdeterminations of P. digitalis than of P. pallidus.