Weak-leaf Bur Ragweed

Ambrosia confertiflora

Bur Ragweed, Ambrosia confertifolia, photo © by Michael Plagens

Photographed along Rackensack Wash near Camp Creek, Maricopa Co., Arizona, Oct 2009.

Brown ambrosia aphid colonies can sometimes be found on these plants, but generally only if ants are present to guard them. The aphids are then predated by Convergent Lady Birds.

Brown Ambrosia Aphid  Wood Ant  Convergent Lady Bird 

PERENNIAL HERB: Re-grows from underground rhizomes which spread out thus forming colonies of this plant. Mostly less than ½ meter tall

LEAVES: Pale green leaves are twice, or more, pinnately dissected into narrow segments.

RANGE: In the Sonoran Desert found in canyons, near riparian habitats, in mesquite bosque openings, mostly at the higher elevations. Common also in high desert habitats such as juniper woodlands, chaparral and grasslands. Widely distributed from California east into south-central USA. This plant flourishes best in soils that have been disturbed by human activities like off road vehicles, agriculture and heavy foot traffic.

FLOWERS: Flowering may occur in late spring and again in late summer and fall depending on rainfall. The greenish flowers are not showy, but the copious pollen dispersed by the wind is responsible for hay fever symptoms in many people. On the spikes female flower heads are below the smaller exclusively male-flowered heads above. In the photo below each male flower head holds about ten florets - the yellow color is the pollen ready to be carried away by breezes.

FRUIT: The seeds are enclosed in a weak bur.

UNARMED. No thorns, burrs have weak barbs.

Asteraceae -- Sunflower Family

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Bur Ragweed, Ambrosia confertifolia, photo © by Michael Plagens

More Information:

Sonoran Desert Field Guide
Sonoran Desert Places
Sonoran Desert Naturalist Home Page


Copyright Michael J. Plagens, page created 16 October 2009,
updated 6 Aug. 2015.