Arizona Naturalists >>> Ponderosa Woodland Flora >>> Asteraceae >>> Ambrosia acanthicarpa

Flatspine Bur Ragweed

Ambrosia acanthicarpa

Arizona Thistle, Cirsium arizonicum, photo © by Mike Plagens

Observed in the ponderosa forest near the campus of Northern Arizona University in Flagstaff, Coconino Co., Arizona, USA. August 2009.

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FLOWERS: The greenish flowers turn yellow by virtue of abundant pollen (hayfever antigen). In spikes with separate male and female flowerheads.

FRUIT: The bracts enclosing the seed soon form large, purplish color spines that are noticeably flattened.

LEAVES: Leaves are deeply divided into narrow segments and are very similar to other ragweed species.

ANNUAL: Few plants surpass one meter in height and there are usually several branching stems from base.

RANGE: Common in Arizona's ponderosa woodlands after good summer rains. Found in relatively moist habitats through much of western North America.

UNARMED. The bur points are a slightly sharp.

Asteraceae -- Sunflower Family

More Information:

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Arizona Naturalist
Arizona's Ponderosa Woodlands
The Flora of Arizona's Ponderosa Woodlands


Copyright Michael J. Plagens, 1999-2010