Amsonia hirtella Standley; A. hirtella var. pogonosepala (Woodson) Wiggins

Stems erect, 23–62(–80) cm, glabrous or moderately (some­what densely or sparsely) pubescent; branches usually borne on distal portion of stem (occasionally below midpoint), not or slightly exceeding infructescence. Leaves: pet­iole 0–2(–3) mm, glabrous or moderately (sparsely) pubescent; blades heteromorphic or all very narrow; stem leaf blades narrowly oblong-elliptic to narrowly oblong, narrowly lanceolate, or linear, 4.5–7.5(–9.2) cm × 2–18 mm, margins entire, sometimes slightly revolute, moderately short-ciliate if leaf blade is pubescent, apex acute to acuminate, surfaces glabrous or moderately (sparsely) pubescent; branch leaf blades very narrowly lanceolate or very narrowly elliptic to linear, 3.5–6(–6.8) cm × 1–5(–7) mm. Flowers: sepals narrowly del­tate to subulate, (2–)3–5(–7) mm; corolla tube bluish or purplish green or green, 7.5–12(–17) mm, lobes white to blue or yellowish white, (2.5–)3–5(–7) mm, outer sur­face of corolla glabrous. Follicles erect, 2–10(–13) cm × 2–4 mm, apex acuminate, glabrous. Seeds 6–10 × 1–2.5 mm.

Flowering spring; fruiting late spring–summer. Rocky hillsides, arroyos and draws, woodlands, washes and flood plains; 600–1900 m; Ariz., N.Mex., Tex.; Mexico (Chihuahua, Sonora).

Leaf morphology and pubescence are quite variable in Amsonia palmeri; if stem leaves are broad, then the plant is noticeably heterophyllous at maturity with narrow branch leaves. Glabrous and pubescent individuals often occur in mixed populations (S. P. McLaughlin 1982). The species can be distinguished from A. tharpii in part by the adaxial base of the corolla lobes being glabrous (vs. frequently pubescent in A. tharpii). Amsonia palmeri is fairly widespread in Arizona, especially in southern and western counties, but is confined to limited portions of southwestern New Mexico and western Texas.