Stalks at first unbranched, later with many flowering side branches. Flowers in dense racemes, terminal, with slender, leaflike bracts; arise from upper leaf axils; of typical lobelia shape with 2-parted upper lip and prominent, 3-divided lower lip; to 1 inch long; with protruding stamens; cardinal-red, rarely vermillion, very rarely white or pink. Blooms July–October. Leaves alternate, numerous, dark green, to 6 inches long, lance-shaped, finely toothed. Fruits capsules, ribbed lengthwise, with a crown of withered flower parts persisting at the tip.