Herbs, annual or perennial. Stems erect, hairy [glabrous]. Leaves cauline, opposite [alternate distally]; petiole absent; blade not fleshy, not leathery, margins serrate to subentire [entire]. Inflorescences terminal, racemes [thyrses or flowers solitary]; bracts present. Pedicels present; bracteoles absent [present]. Flowers bisexual; sepals 5, basally connate, calyx slightly bilaterally symmetric, campanulate to rotate, lobes lanceolate; corolla purple, mauve, or white, bilaterally symmetric, bilabiate, short-tubular [globular], not spurred, tube with a pair of rounded sacs at base of median lobe abaxially, lobes 5, abaxial 3, adaxial 2, adaxial lip with concave palate at base containing a cylindric, 2-fid tooth [ridge]; stamens 4, basally adnate to corolla, didynamous, filaments glandular-hairy [glabrous]; staminode 0; ovary 2-locular, placentation axile; stigma punctiform. Fruits capsules, dehiscence loculicidal. Seeds 10–50, light brown to brown, prismatic, wings absent. x = 10.
Introduced; Fla., Mexico, West Indies, Central America, South America, introduced also in Asia, Africa, Pacific Islands.
Species 25 (1 in the flora).