Stems erect, 16–60 cm, glabrous or sparsely to moderately pubescent; branches often borne on most of stem (or only distal portion), often remaining shor­ter than infructescence. Leaves: petiole 0–2.5 mm, glabrous or sparsely to moderately pubes­cent; blades slightly hetero­morphic; stem leaf blades linear to ligulate (very narrowly elliptic or lanceolate), (2.3–)3–6.5(–9) cm × (0.7–)1–2.8(–5) mm, margins entire, sometimes some­what revolute, ciliate or not, apex narrowly acute, surfaces glabrous or sparsely to moderately pubescent; branch leaf blades linear, (1.1–)2.5–5.2(–7) cm × 0.5–1.3(–3) mm. Flowers: sepals narrowly deltate (to subulate) with weak, often curved apex, (2–)3.5–7(–9.5) mm; corolla tube bluish to lead-colored, lavender or purplish below, often greenish above, (20–)28–41(–45) mm, lobes white to cream or bluish white (pale pink), (6.5–)9–13.5(–18) mm, outer surface of corolla glabrous. Follicles erect, (3.8–)6–11(–20) cm × (2.4–)2.9–4 mm, apex short-acuminate (acute), glabrous. Seeds 5.3–8.1(–10.5) × 1.5–2.7 mm.

Varieties 2 (2 in the flora): sc United States, n Mexico.

The varieties of Amsonia longiflora are distinguished by differing pubescence. Both are generally found on lime­stone substrates. Notes on a specimen collected by R. C. Sivinski (Sivinski 4282, UNM) indicate that var. longiflora was collected on dolomite and had pale blue corollas, whereas nearby var. salpignantha occurred on gypsum and had white to pale pink corollas (the latter is rarely reported, and corolla lobe color is not consistently different between the two varieties). It is not known whether this substrate preference may be consistent and contributes to maintaining the distinction between the two. Both are restricted to southern New Mexico and Texas, but var. longiflora is confined to a relatively small portion of western Texas, while var. salpignantha is more widely distributed in western Texas, and occurs also in several counties in a disjunct portion of central Texas.

Lower Taxa

• Amsonia longiflora var. longiflora
• Amsonia longiflora var. salpignantha (Woodson) S. P. McLaughlin