Herbs, annual, biennial, or perennial, often decumbent at base or sometimes cespitose. Taproots slender or often stout, deep, branched caudex often present, some species stoloniferous or rhizomatous. Stems simple or branched, terete or sometimes angular. Leaves opposite or occasionally whorled, connate proximally, petiolate (basal leaves) or sessile (most cauline leaves); blade 1–5-veined, linear to obovate or spatulate, herbaceous, apex acute to obtuse. Inflorescences terminal or sometimes axillary, simple or branched, sometimes condensed cymes, frequently flowers few or solitary, frequently glandular-pubescent and viscid; bracts paired, herbaceous or scarious, or absent; involucel bracteoles absent. Pedicels erect, rarely flowers sessile or subsessile. Flowers bisexual, sometimes unisexual (rarely so on separate plants); sepals connate proximally into tube, (4–)10–28(–40) mm; tube green, whitish, and/or purplish, 10–30-veined, cylindric to campanulate, urceolate, or clavate, terete, frequently inflated, membranous or more rarely herbaceous, commissures between sepals 1-veined, herbaceous; lobes green or purplish, 1–5-veined, broadly triangular to lance-oblong or linear, usually shorter than tube, margins whitish, scarious, apex acute to obtuse; petals 5, white, pink, scarlet, dusky purple, or off-white tinged with purple, clawed, claw usually conspicuous, sometimes small, rarely absent, auricles 2, coronal appendages 2, variously shaped or dissected; limb usually exserted and conspicuous, oblanceolate to obovate, apex 2-lobed, sometimes dissected into 1–4 linear lobes or irregular teeth, or fimbriate, rarely entire; nectaries at filament bases; stamens 10, rarely fewer or absent, frequently dimorphic with longer opposite petals, arising with petals from carpophore; filaments distinct nearly to base; staminodes absent (rarely to 10 in pistillate flowers, arising with petals from carpophore, filiform); ovary 1- or 3–5-locular; styles 3 or 5, occasionally 4 (absent in staminate flowers), filiform, 1.5–20 mm, glabrous proximally; stigmas 3 or 5, occasionally 4, linear along adaxial surface of styles, papillate (30×). Capsules ovoid to globose, opening along sutures into 3–5 valves, frequently splitting into 6–10 equal teeth; carpophore usually present. Seeds ca. (5–)15–100(–500+), reddish to gray or black, reniform to globose, usually tuberculate or papillate, papillae around margins sometimes larger and inflated, marginal wing sometimes present, appendage absent; embryo peripheral, curved. x = (10) 12.