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Common Ragweed, Annual Ragweed, Small Ragweed, Roman Wormwood - Ambrosia artemisiifolia


Family: Asteraceae – Aster family Genus Common Name: Ragweed Native Status: Native
Ambrosia artemisiifolia - Common Ragweed, Annual Ragweed, Small Ragweed, Roman Wormwood. The leaves and stem of Common Ragweed are hairy. The leaves are deeply lobed and quite ragged. The inflorescence is a slender, almost candle-like cluster at the end of the stems. The upper flowers are usually male; the lower flowers female.

The ragweeds generally cause much hayfever, allergic reaction, and asthma exacerbation due to their tiny airborne pollen, which can drift and be inhaled far from the source plant. Because of this, other plants which bloom at the same time, such as Goldenrod, frequently get blamed for ragweed-caused hayfever.

Common ragweed is found in every state in the United States except for Alaska, and is found in most of Canada. While it is an introduced species in Hawaii, it is native to continental North America. Two varieties of the plant are native to the eastern United States; a variety found in the all but a few southeastern states is native to Canada but not to the United States, according to the USDA Plants Database. It is officially listed as a noxious weed in Illinois, Michigan, and Oregon, and is thus legally controlled. It is considered a weed due to agricultural considerations in much of the United States.

Found in:
AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, HI, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY

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Distribution of Ambrosia artemisiifolia in the United States and Canada:
USDA Plants Distribution Map temporarily unavailable.
Blue=Native; Grey=Introduced

Map from USDA Plants Database:
USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov, 20 Jan 2017). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

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Site: Walker County, GA Date: 2011-September-04Photographer: Gerald C. Williamson
Nikon D7000
These are the male blossoms from which the hayfever-causing pollen is emitted.
Ambrosia artemisiifolia

Site: Walker County, GA Date: 2011-September-04Photographer: Gerald C Williamson
Nikon D7000
Common Ragweed is a highly branching plant, with new branches forming at the leaf nodes. It grows to be up to about 7 feet tall.
Click on the photo for a larger image
Ambrosia artemisiifolia

Site: Walker County, GA Date: 2011-September-04Photographer: Gerald C Williamson
Nikon D7000
The leaves of Ambrosia artemisiifolia are very deeply lobed. I suspect that these ragged leaves are the source of the “ragweed” common name.
Click on the photo for a larger image
Ambrosia artemisiifolia

References used for identification and information:

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2017
Photographs Copyrighted by the named photographer