Index Seminum (Frankfurt) 1836: 4. 1838.
Annuals, 30–120 (–200) cm. Stems erect, strictly, if at all, branched. Leaves cauline; mostly opposite (distal sometimes alternate); petiolate; blades (3–5-nerved) ± deltate, ovate, or rhombic (proximal 1–3 pairs, often 3–5-lobed), margins usually toothed, faces densely to sparsely scabrellous to strigillose (abaxial often canescent), both usually glanddotted. Heads ± disciform, in (± ebracteate) paniculiform arrays. Involucres turbinate to hemispheric, 3–5+ mm diam. Phyllaries persistent, 10–12+ in 2+ series, distinct, outer 5 herbaceous, inner scarious to membranous. Receptacles convex to conic; paleae spatulate to linear, ± membranous, sometimes 0. Pistillate florets 5; corollas whitish, tubular, or 0. Functionally staminate florets 5–10 (–20+); corollas whitish, funnelform, lobes 5, erect (filaments connate, anthers distinct). Cypselae plumply obovoid to obcompressed, finely striate, sparsely strigillose or hispidulous distally, little, if at all, glanddotted; pappi 0. x = 18.
North America, in Europe