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.