Amsonia illustris Woodson, Ann. Missouri Bot. Gard. 16: 407. 1929

Stems erect, 49–88 cm. Leaves: petiole (3–)4–7 mm, sparsely to moderately pubescent with long, soft hairs or glabrous; stem leaf blades lanceolate (narrowly elliptic), (5.7–)7–12.5(–14.4) cm × 12–26(–31) mm, margins entire, weakly or not revolute, often ciliate with long, soft hairs (rarely weakly, irregularly crenulate), apex acuminate to acute, surfaces sparsely pubescent with long, soft hairs, especially on midrib, adaxially or on both surfaces, or glabrous. Flowers: sepals narrowly deltate to deltate, (0.5–)0.9–1.6(–1.9) mm, usually mostly sparsely to moderately long-pubescent, rarely all or most in an inflorescence glabrous, often glabrescent or glabrate in fruit; corolla tube 6.5–8 mm, lobes (6–)7.5–9.8(–10.5) mm. Follicles erect to pendulous, (7–)10–15 cm × 2.1–3.4(–4.2) mm. Seeds 6–8(–10.4) × (1.2–)1.5–1.7(–3.3) mm. 2n = 22.

Flowering spring (rarely summer); fruiting summer (rarely fall). Gravel bars, stream beds and banks, flood plains and wetlands, low woods, glades and barrens, ditches, railroad embankments, old fields; 0–400 m; Ark., Ill., Kans., Mo., Okla.

Variety illustris is characterized by narrow leaves and pubescent calyces; it is confined to the western portion of the range of Amsonia tabernaemontana.