3. Ruellia L.

Plants perennial. Aerial stems spreading or ascending, unbranched or branched. Inflorescences few-flowered clusters, these either nearly sessile in the axils of main stem leaves or associated with reduced leaves at the tip of an axillary branch (inflorescence stalk). Flowers subtended by bracts 1–12 mm long, these shorter than the calyx, linear to narrowly elliptic or oblanceolate. Calyces deeply lobed, the lobes 10–30 mm long, sharply pointed at the tip. Corollas nearly actinomorphic, with a slender tube expanded fairly abruptly into 5 lobes, glabrous or hairy, light purple to lavender, rarely white. Stamens 4, usually included in the corolla throat, the anther sacs similar in size and parallel. Staminodes usually absent, rarely 1. Fruits narrowly oblong-elliptic or club-shaped, the valves ascending to arched outward after dehiscence. Seeds (4–)6–16, 2.5–3.5 mm in diameter, more or less circular in outline, somewhat flattened, reddish brown to brown, usually somewhat sticky when fresh and appearing minutely hairy when moistened. About 250 species, nearly worldwide, mostly in tropical and warm-temperate regions.

The last monographer of Ruellia in eastern North America, M. L. Fernald (1945), divided most of the species into a number of infraspecific taxa, based on differences in flower color, pubescence, presence of cleistogamous flowers, and corolla length. Some recent students of the genus (Long, 1970; Turner, 1991) have suggested that most of these taxa intergrade too much to allow recognition, and although Steyermark (1963) accepted several varieties and forms for the Missouri species, he also noted that widespread intermediates made recognition of infraspecific taxa difficult. Accordingly, the varieties and forms treated by Steyermark are not accepted in the present treatment.