Several taxa are cultivated, and our wild species are at least as attractive as many of the exotic ones. The lower lip, 3-lobed, is anatomically the upper one, as the flower twists on its pedicel 180° in development (just as in most orchids). Unlike many plants with milky juice, lobelias last very well when cut and placed in water. They are ± poisonous if taken internally, and some species, e.g., L. inflata, were used medicinally in the past.
1. Principal cauline leaves (if any) linear to linear-lanceolate (or linear-oblanceolate), entire to remotely denticulate, the widest less than 0.4 (–0.7) cm broad.
2. Leaves all basal (sometimes a few tiny bracts on stem), usually submersed, somewhat fleshy (consisting of 2 hollow tubes).
2. Leaves all or mostly cauline, thin (not tubular in construction).
3. Calyx lobes at least twice as long as the calyx tube and inferior part of the ovary at anthesis; plant a rare escape from cultivation, diffuse or partly trailing; pedicels without bracteoles, much exceeding their subtending bracts.
3. Calyx lobes mostly less than twice as long as the calyx tube and inferior part of the ovary; plant a common native calciphile, ± stiffly erect; pedicels each with a pair of tiny bracteoles near the middle, often scarcely if at all exceeding their subtending bracts.
1. Principal cauline leaves elliptic to oblanceolate or obovate, ± toothed or crenulate (or at least denticulate), (0.7–) 1–4.5 (–6) cm broad.
4. Mature corolla 1.8–4 (–4.3) cm long, with an open slit on each side near the base of the tube.
5. Corolla bright red (except in albinos), at least 3 cm long; calyx lobes glabrous, not auriculate.
5. Corolla bright blue (except in albinos), less than 2.4 (–2.6) cm long; calyx lobes bristly-ciliate, auriculate at base.
4. Mature corolla less than 1.3 cm long, without lateral slits.
6. Stem ± hairy throughout, with many of the hairs 0.5–1 mm long; calyx lobes usually less than twice as long as inferior ovary at anthesis; capsule wholly inferior, much inflated at maturity.
6. Stem mostly glabrous or glabrate, usually becoming minutely but densely pubescent toward the base with hairs not over 0.5 mm; calyx lobes at least twice as long as inferior part of the ovary (less as ovary expands); capsule only about 1/2–3/4 inferior, not inflated.