Ambrosia

Glandular, aromatic, annual or perennial herbs or shrubs. Leaves sessile or petiolate, mostly opposite, often alternate above, lobed to bipinnate. Capitula dimorphic, many, small. Male capitula virtually hemispherical, few-many, drooping, in leafless terminal spikes or racemes; involucral bracts connate, few, 1-seriate; receptacle with scales; florets tubular, 5-lobed; anthers obtuse at base, with a short often inflexed terminal appendage; style short, entire. Female capitula campanulate, few, sessile, solitary or a few clustered together in upper leaf-axils below males; involucral bracts connate, few, 1-seriate, beaked, ribbed or prickly in fruit; floret solitary, lacking a corolla; style with elongate, linear, papillose branches. Cypselas ovoid, smooth, retained inside nut-like involucre; pappus absent.