Description: Aromatic and glandular annual and perennial herbs.
Leaves lobed to deeply dissected, opposite or alternate, ± glabrous to hairy.
Heads inconspicuous, unisexual, receptacle with scales. Male heads few to many in bractless terminal spikes or racemes; heads cup-shaped, involucral bracts fused, in several rows; corollas funnelform-campanulate, 5-toothed, ovary and pappus absent; anthers ± obtuse at the base, terminal appendage often inflexed. Female heads sessile in upper leaf axils, below male heads; heads vase-shaped with a few fused involucral bracts in 1 row, becoming hardened, beaked and ribbed when in fruit; 1–7 florets consisting of ovary and style only; style branches elongate, linear, papillose.
Achenes ovoid, smooth, retained inside the nut-like involucre (the fruit); pappus absent.
Distribution and occurrence: World: c. 40 species, North & South America, Mediterranean. Australia: 4 species (naturalized), N.S.W., Vic, S.A., W.A.
Text by L. Murray
| ||Key to the species|| |
|1||Leaves pinnatifid, with triangular lobes||Ambrosia psilostachya|
|Leaves 2- or 3-, sometimes 4-pinnate, lobes not triangular||2|
|2||Female heads abundant in massive clusters; fruit covered in short hooked spines||Ambrosia confertiflora|
|Female heads few in small clusters; fruit without hooked spines|
Back to 1
|3||Fruit glabrous; leaves green-grey; annual||Ambrosia artemisiifolia|
|Fruit hairy; leaves with a grey lacy appearance; perennial|
Back to 2