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Genus Ambrosia Family Asteraceae

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
Taxon concept:

 Key to the species 
1Leaves pinnatifid, with triangular lobesAmbrosia psilostachya
Leaves 2- or 3-, sometimes 4-pinnate, lobes not triangular2
2Female heads abundant in massive clusters; fruit covered in short hooked spinesAmbrosia confertiflora
Female heads few in small clusters; fruit without hooked spines
                       Back to 1
3
3Fruit glabrous; leaves green-grey; annualAmbrosia artemisiifolia
Fruit hairy; leaves with a grey lacy appearance; perennial
                       Back to 2
Ambrosia tenuifolia

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