1. Physostegia angustifolia Fernald (false dragonhead)

Pl. 439 a–c; Map 1978

Plants sometimes with rhizomes. Stems 40–170 cm long, with 9–18 nodes below the inflorescence. Leaves progressively shorter toward the stem tip, the foliage leaves grading into the inflorescence bracts, the inflorescences frequently often appearing elevated from the foliage, then with 2 to several pairs of short or elongate, usually widely spaced (10–50 mm apart), empty bracts. Blades of main foliage leaves 3–20 cm long, 3–9(–12) mm wide, relatively thick and stiff, the lowermost blades sometimes lanceolate to oblanceolate, those of the median and upper leaves mostly narrowly oblong-lanceolate or narrowly oblong-oblanceolate to linear, sometimes with small basal auricles that clasp the stem, more commonly angled to a truncate or abruptly rounded base as wide as or slightly wider than the stem node, the margins sharply but finely toothed, the teeth sometimes relatively few and/or only toward the blade tip. Axes of the inflorescences with 2 kinds of pubescence: dense, minute hairs (visible at 10× magnification only as minute nubs or slender tubercles to 0.05 mm long) and sparse to moderate, minute but distinctly longer (0.1–0.2 mm long), slender hairs. Bracts 4–7 mm long (except sometimes the empty basal bracts longer), mostly shorter than the calyces at flowering, lanceolate to ovate. Calyces mostly somewhat overlapping along the inflorescence axis, 6–8 mm long at flowering, becoming enlarged to 8–12 mm at fruiting, the outer surface densely pubescent with very minute hairs. Corollas (15–)20–30 mm long, white to pale lavender, occasionally pinkish-tinged or light pink. Nutlets 2.0–3.0(–3.5) mm long. 2n=38. June–September.

Scattered, in the Unglaciated Plains, Ozark, and Ozark Border Divisions, north locally to Lincoln County (Kansas to Texas east to Illinois, Tennessee, and Georgia). Upland prairies, glades, tops of bluffs, mesic to dry upland forests, and occasionally banks of streams and bottomland forests; also ditches, roadsides, and disturbed areas.

On the whole, this is a less variable species morphologically than the closely related P. virginiana. Cantino (1982) noted that the pubescence of the inflorescence axis is the only stable character to separate this species from P. virginiana rangewide. Users of the key should not obsess over measuring the lengths of the hairs. The critical feature is that the hairs in P. angustifolia occur in two size classes not the absolute lengths of the two kinds of hairs. In Missouri, occasional plants of P. virginiana growing in fens are reduced and take on the appearance of P. angustifolia. Such individuals with narrow leaves and apparently well-elevated inflorescences still have the pubescence of the inflorescence axis characteristic of P. virginiana.