Annual, perennial, herbs or subshrubs, rarely small trees. Stems often purplish, erect or decumbent, usually branched in the upper part or ± throughout. Leaves simple, opposite, petiolate or sessile, lamina often 3–nerved, oblong–ovate to lanceolate or linear, margins entire, serrate or spinulose–serrate. Capitula radiate or discoid, usually in tight or loose flat topped glomerules, forming ± corymbiform synflorescence. Involucre oblong, urceolate, cylindric, or turbinate. Phyllaries persistent, 2–6, uniseriate, linear, concave, or boat–shaped, subequal, free. Receptacle flat to convex, epaleate or sometimes bristles present. Ray florets 0–1(–2), female, fertile, ligules yellow. Disc florets 1–15,  bisexual, fertile; corollas yellow, tube shorter than or equalling to funnelform – campanulate, 5–lobed limb, lobes ± deltate. Cypselas black, weakly compressed, narrowly oblanceolate or linear–oblong, usually 8–10 (–11) ribbed, glabrous. Pappus usually absent, rarely of 2–4, hyaline, persistent, scales or coroniform (of connate scales).

A small genus of 22 species, native to North America, widely distributed and naturalized in most of the tropical and subtropical regions of the world. Represented in Pakistan by the following naturalized species: