These are familiar plants to those who note the colorful flowers late in summer or who play with the fruit, a capsule that, at maturity, dehisces explosively when touched, scattering the seeds. The flower structure is highly modified, although it is clearly bilaterally symmetrical. There are three sepals, of which the two upper (lateral) ones are small but the lower one large, petaloid, sac-like, and slender-spurred. The petals appear to be 3, each of the two lateral ones with a lobe presumably representing a fused petal. White-flowered forms may occur in any of our species, and all are variable in color and marking. Seedlings of our two native species are often abundant in moist places, looking pale and watery, with rather rounded or crenate teeth, but are impossible to distinguish in the absence of flowers. All our species are annuals.
1. Leaf blades sharply toothed, teeth ± gland-tipped; flowers usually red (pink) to purple; rare escapes from cultivation into disturbed places.
2. Stem ± pubescent; flowers axillary on main stem; petiole bearing prominent saucer-like glands below the blade; fruits pubescent; leaves uniformly alternate.
2. Stem glabrous; flowers in terminal or axillary inflorescences; petioles eglandular or with ± glandular teeth at base of decurrent blade; fruits glabrous; distal leaves often opposite or whorled.
3. Corolla tubular and clearly 2-lipped; spur sharply recurved, much shorter than corolla; upper leaves usually whorled; tall plants (mostly 1–2 m).
3. Corolla flat, nearly regular; spur arching, as long as to even exceeding corolla; upper leaves alternate or opposite; plants normally under ca. 5 dm tall.
1. Leaf blades with rather rounded teeth (their tips obscure), crenate in aspect and only ca. 12 (–15) or fewer per side; flowers orange or yellow; native species, usually in moist places.
3. Flowers orange (rarely yellow); mature spur ca. (7–) 9–10 (–12) mm long; sac of spurred sepal usually distinctly longer than broad.
3. Flowers yellow; mature spur ca. 5 mm long or less; sac of spurred sepal about as broad as long or broader.