Plants annual or perennial, emersed, floating-leaved, or rarely submersed, glabrous to stellate-pubescent; rhizomes present or absent; stolons absent; corms absent; tubers absent. Roots not septate. Leaves sessile or petiolate; petioles triangular, rarely terete; blade with translucent markings as dots or lines present or absent, linear to lanceolate to ovate, base attenuate to cordate, margins entire or undulating, apex obtuse to acute. Inflorescences racemes or panicles, rarely umbels, of 1--18 whorls, erect or decumbent, emersed; bracts coarse, apex obtuse to acute, surfaces smooth or papillose along veins, apex obtuse to acute. Flowers bisexual, subsessile to pedicellate; bracts subtending pedicels, subulate to lanceolate, shorter than to longer than pedicels, apex obtuse to acute; pedicels ascending to recurved; receptacle convex; sepals recurved to spreading, herbaceous to leathery, sculpturing absent; petals white, entire; stamens 9--25; filaments linear, glabrous; pistils 15--250 or more, spirally arranged on convex receptacle, forming head, distinct; ovules 1; style terminal or lateral. Fruits plump, often longitudinally ribbed, sometimes flattened, rarely abaxially keeled, abaxial wings absent, lateral wings absent, glands often present.
Fls perfect; receptacle elevated, convex or globose; sep 3, persistent, sometimes accrescent; pet 3, white, deciduous; stamens 6-30; filaments elongate; pistils borne in several series and aggregated into a globose head; achenes turgid, evenly ribbed or ridged; scape erect or prostrate, bearing an infl of 1-many verticils of fls, sometimes branched from the lower verticils; verticils 3-bracted and commonly with additional bracteoles. (Helianthium) 20+, widespread, mainly tropical.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.