Plants perennial herbs (shrubby or functionally annual elsewhere), with fibrous roots, sometimes with rhizomes. Stems branched, sometimes somewhat swollen toward the base, glabrous or minutely hairy, the hairs without pustular bases. Thorns often present, these solitary or rarely paired, positioned in the leaf axils, 4–15 mm long, straight, slender. Leaves alternate, well-developed. Stipules absent. Leaf blades simple, sessile or tapered to an often winged petiole, the surfaces glabrous or minutely, the hairs without pustular bases and not roughened to the touch, the margins entire or less commonly minutely toothed, sometimes also slightly wavy or minutely hairy. Inflorescences axillary or terminal, appearing as clusters or leafy panicles, not appearing coiled (scorpioid), seldom of solitary axillary flowers, some of the flowers appearing subtended by small leaflike bracts. Flowers actinomorphic, hypogynous, perfect; cleistogamous flowers not produced. Calyces very deeply 5-lobed, the lobes equal or nearly so, narrowly to broadly lanceolate and somewhat overlapping toward the base, persistent and becoming somewhat enlarged at fruiting. Corollas deeply 5-lobed, broadly bell-shaped to nearly saucer-shaped, blue to less commonly purplish blue (rarely white), sometimes greenish white near the base. Stamens 5, the filaments abruptly broadened at the base and attached near the base of the short corolla tube, the anthers more or less exserted, appearing 4-locular, attached near the dorsal midpoint, usually blue. Pistil 1 per flower, of 2 fused carpels. Ovary superior, unlobed, 2(–4)-locular and with numerous ovules per locule, the placentation axile. Styles 2(–4), situated at the tip of the ovary, elongate, entire, usually persistent at fruiting, the stigmas somewhat funnel-shaped or wedge-shaped. Fruits capsules, dehiscent longitudinally, either irregularly or more or less with 2 valves. Seeds numerous, 0.5–0.6 mm long, ovoid to nearly cylindrical, the surface with several longitudinal ridges, tan to brown, glabrous. About 11 species, eastern U.S. to South America, Caribbean Islands, Asia, Africa, most diverse in tropical or warm-temperate regions.