Plants annual, with slender taproots (perennial herbs or low shrubs, sometimes with rhizomes or stolons, elsewhere). Stems erect or strongly ascending, slender, sharply 4-angled, unbranched or branched mostly below the midpoint, hairy. Leaves sessile or short-petiolate, the petiole winged toward the tip, with a slight to moderate minty fragrance when crushed. Leaf blades variously shaped, those uppermost on the stems usually somewhat reduced, the margins entire or few-toothed, the surfaces glabrous or more commonly hairy, also with sometimes conspicuous, sessile glands. Inflorescences axillary, small clusters of (2–)8–12(–20) at nearly every node, the flowers short-stalked, the stalk with a pair of short, linear to narrowly lanceolate bractlets at the base. Cleistogamous flowers sometimes produced, these with calyces similar to those of open flowers, but corollas that are only about as long as the calyx lobes and never fully open. Calyces zygomorphic, lacking a lateral projection, somewhat pouched along 1 side at the base, more or less cylindric, the tube strongly 13-nerved (-ribbed), with a fringe of short, bristly hairs in the mouth, 2-lipped, the lobes shorter than to about as long as the tube, the upper lip deeply 3-lobed and sometimes spreading upward, the lower lip deeply 2-lobed and straight to slightly arched upward, the lobes narrowly triangular to nearly linear, not spinescent, not becoming enlarged and papery at fruiting. Corollas (except in cleistogamous flowers) zygomorphic, lavender to pale bluish purple or nearly white, the lower lip sometimes with lighter or darker spots or mottling toward the base, the outer surface moderately short-hairy, the tube narrowly funnelform to nearly cylindric, relatively shallowly 2-lipped, the upper lip unlobed or shallowly notched, straight to slightly concave, the lower lip slightly concave (slightly scoop-shaped) to somewhat spreading, 3-lobed, the central lobe sometimes shallowly notched. Stamens 2 (a pair of small staminodes often also present), not exserted (ascending under the upper lip; somewhat exserted elsewhere), the anthers small, the connective short, the pollen sacs 2, spreading (parallel elsewhere), white or pinkish-tinged. Ovary deeply lobed, the style appearing nearly basal from a deep apical notch. Style not exserted, unequally 2-branched at the tip. Fruits dry schizocarps, separating into usually 4 nutlets, these 0.7–1.5 mm long, oblong-obovoid or oblong-ellipsoid to nearly spherical, the surface yellowish brown to dark brown or black, smooth or finely pebbled, glabrous, sometimes somewhat glaucous, otherwise somewhat shiny. Thirty-eight species, North America, South America.