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Annual or perennial erect or prostrate hairy herbs. Leaves opposite, sessile or shortly petiolate, mostly ovate, elliptic or oblong, the lateral nerves evident; stipule-sheath connate with the petioles, bearing several fimbriae. Flowers hermaphrodite or said sometimes to be polygamo-dioecious, not heterostylous, small, in dense terminal heads enclosed in an involucre formed of (2–)4 leaves which are several-nerved from the base. Calyx-tube turbinate or subglobose, the limb deeply lobed; lobes 4–8, lanceolate, ovate or subulate, persistent. Corolla shortly funnel-shaped; lobes 3–5, ovate to lanceolate; throat glabrous but tube with a narrow area of hairs inside near the base. Stamens with anthers exserted. Style filiform; stigmas 3–4, linear or spathulate, exserted. Ovary 3–4-locular; ovules solitary, affixed to the middle of the septum. Capsule 3–4-coccous, crowned by the persistent calyx, eventually splitting into separate cocci, sometimes leaving a very small persistent axis. Cocci mostly obovoid, smooth or more often muricate or papillose. Seeds oblong-ellipsoid or obovoid, dorsally convex, ventrally with 2 grooves; endosperm corneous.
Plants herbaceous, the stems terete, usually densely pubescent. Leaves with the blades usually wide; stipules adnate to the petioles, the sheath multisetose. Inflorescences terminal, capitate, sessile, subtended by conspicuous foliose in-volucral bracts. Flowers with the calycine cup turbinate or subglobose, the lobes 4-8, connate. Fruits partly superior, dry, the cocci indehiscent; seeds with the strophiole very narrow and short, the cells of the testa isodiametric to contorted.
Fls 4–8-merous; sep foliaceous, ± connate at base; cor funnelform, with short lobes; stamens included; ovary (2)3–4(–6)-locular, with a single axile ovule in each locule; fr separating into (2)3–4(–6) nutlets; herbs, mostly diffusely branched, with fls in terminal involucrate glomerules. 15, trop. Amer.
