Herbs, annual or perennial, finely pubescent, often somewhat viscid; taproot slender and soft to stout and woody (depending on duration). Stems procumbent, often clambering through other vegetation, unarmed, without glutinous bands on internodes. Leaves paired, petiolate, unequal, blades thin, base ± asymmetric. Inflorescences axillary, pedunculate, clusters of 3 simultaneously blooming flowers resembling single flower; bracts persistent, not accrescent, 3, forming involucre, distinct, broadly ovate, cucullate, thin, translucent. Flowers bisexual, chasmogamous; perianth strongly bilaterally symmetric, funnelform but strongly oblique, constricted beyond ovary, gradually expanded, adaxial lobes minute, abaxially forming a fan-shaped limb; stamens 4-7, ± exserted; styles exserted beyond stamens; stigmas capitate. Fruits oblong to somewhat obovate, dorsoventrally compressed (adaxial face convex, internal, in inflorescence), with 5 strongly modified ribs, central adaxial rib an inconspicuous to pronounced rib or ridge, sometimes toothed, keeled, coriaceous; 2 lateral ribs expanded and incurved toward concave side as wings or teeth; 2 ribs on concave surface forming low, thin ridge, often with teeth that usually bear glands at tip, surface glabrous, and smooth or the adaxial slightly rugose.
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