1 Corolla tube 25-40 mm long, sharply constricted at the orifice; [subgenus Sphinctosiphon; section Longiflorae]

1 Corolla tube 6-9 mm long, not constricted at the orifice; [subgenus Amsonia].

  2 Corolla glabrous on the outer surface; stem pubescent (A. ciliata) or glabrous (A. rigida); [of the Coastal Plain from se. and sc. NC southward and westward to the Interior Highlands and TX].

    3 Leaves elliptic, the lower and upper mostly 3-5× as long as wide, all leaves > 5 mm wide; leaves glabrous; [of seasonally flooded depression wetlands and moist pinelands].

      4 Leaves 6.0-10.0 cm long (mean 7.1); corolla lobes 6.5-8.5 mm long (mean 7.3); [of se. LA to e. TX]

    3 Leaves linear to lanceolate, the lower leaves 4-30× as long as wide, the upper leaves 1 mm or less wide; leaves ciliate; [of dry, sandy habitats, such as sandhills]

        5 Leaves glossy on upper surface; leaf margins not ciliolate; leaves 8-10 cm long; calyx lobes triangular, ca. 1 mm long; [gravel bars in creekbeds and riverbeds in AR and e. OK]

        5 Leaves dull on upper surface; leaf margins ciliolate; leaves 4-5 cm long; calyx lobes linear-triangular, 1.5-2.0 mm long; [dry sandhills, outcrops, glades, prairies, grasslands, collectively more widespread].

          6 Mid and upper stem leaves 1-5 mm wide (occasional specimens to 6 mm), lower and midstem leaves the same width as distal leaves (occasional specimens with lower leaves distinctly broader than upper); [of dry, sandy habitats, such as sandhills, Coastal Plain east of Mississippi River, AND Ozark-Ouachita region west of Mississippi River]

          6 Mid and upper stem leaves (4-) 5-15 mm wide, lower leaves widest, gradually narrowed distally; [OK and TX]

  2 Corolla pubescent on the outer surface; stem glabrous (or sometimes pubescent when young in A. ludoviciana); [more widespread in our area].

             7 Leaf blades densely tomentose below; follicles pubescent; [s. MS west to w. LA, or c. GA]

               8 Leaves ovate lanceolate, 9-11 × 2-4 cm; abaxial leaf surface > 50% obscured by dense pubescence, hoary; trichomes uniform in length and orientation; leaf margin with longer trichomes; corolla tube 6-10 mm long, petal lobes 4.3-7.2 mm long, margins entire; follicles pubescent; [s. MS west to w. LA]

               8 Leaves elliptic ovate, 3-5 × 0.8-1.5 cm; abaxial leaf surface < 50% obscured by dense pubescence, grey-green; trichomes of different lengths, some appressed and curled; leaf margin scabrellous with short hispid trichomes; corolla tube 5.5-8 mm long, petal lobes 4.8-6 mm long, margins undulate; follicles glabrate (glabrous?); [c. GA]

             7 Leaf blades glabrous abaxially or pubescent along midrib and margins (never densely tomentose); follicles glabrous; [collectively widespread].

                 9 Leaves ovate to oblong-elliptic; inflorescence loose, below to barely rising above the leaves, of 15-50 flowers; calyx glabrous; fruits 1-4 pairs per inflorescence

                 9 Leaves narrowly elliptic to linear-lanceolate; inflorescence in compact cluster, ascending above the leaves, from 50-80 flowers; calyx glabrous to pubescent; fruits 5-10 pairs per inflorescence.

                   10 Calyx glabrous

                   10 Calyx pubescent.

                     11 Calyx ciliate, hairs emerging from the margins and or body of the calyx lobes, calyx tube glabrous; adaxial leaf midrib glabrescent; leaves 7-10 cm long; Ozark plateau and the Central forest/grassland transition zone

                     11 Calyx tomentose, hairs emerging from the calyx tube, calyx lobes glabrous; adaxial leaf midrib villous; leaves 5-7 (9) cm long; Texas Blackland Prairies to the Gulf Coast Prairie