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Ambrosia trifida (Great ragweed)
Romfh, Peggy

Ambrosia trifida

Ambrosia trifida L.

Great Ragweed, Giant Ragweed

Asteraceae (Aster Family)



USDA Native Status: L48 (N), CAN (N)

A tall, rough, hairy plant with elongated, terminal clusters of nodding male flower heads above few clusters of female flower heads; some plants with hundreds of heads.

This is the giant among the ragweeds, reaching towering heights and possessing long flower spikes. The pollen of ragweeds is spread by wind rather than by insects. Can be invasive, especially in disturbed areas such as a streambank. Pollen from Great Ragweed contains many antigens that cause hay fever.


From the Image Gallery

17 photo(s) available in the Image Gallery

Plant Characteristics

Duration: Annual
Habit: Subshrub
Size Class: 6-12 ft.

Bloom Information

Bloom Color: Green , Brown
Bloom Time: Jun , Jul , Aug , Sep , Oct


USA: AL , AR , AZ , CA , CO , CT , DC , DE , FL , GA , IA , ID , IL , IN , KS , KY , LA , MA , MD , ME , MI , MN , MO , MS , MT , NC , ND , NE , NH , NJ , NM , NY , OH , OK , OR , PA , RI , SC , SD , TN , TX , UT , VA , VT , WA , WI , WV , WY
Canada: AB , BC , MB , NB , NS , ON , PE , QC , SK
Native Distribution: Throughout much of North America, except far north.
Native Habitat: Waste places, fields, and roadsides.

Butterflies and Moths of North America (BAMONA)

Bordered Patch
(Chlosyne lacinia)

Adult Food Source
Learn more at BAMONA

National Wetland Indicator Status

This information is derived from the U.S. Army Corps of Engineers National Wetland Plant List, Version 3.1 (Lichvar, R.W. 2013. The National Wetland Plant List: 2013 wetland ratings. Phytoneuron 2013-49: 1-241). Click here for map of regions.

From the National Organizations Directory

According to the species list provided by Affiliate Organizations, this plant is on display at the following locations:

Fredericksburg Nature Center - Fredericksburg, TX
Brackenridge Field Laboratory - Austin, TX
Texas Master Naturalists - Lost Pines Chapter - Bastrop, TX
Natural Biodiversity - Johnstown, PA


Bibref 417 - Field Guide to Medicinal Plants and Herbs of Eastern and Central North America (2000) Foster, S. & J. A. Duke
Bibref 1186 - Field Guide to Moths of Eastern North America (2005) Covell, C.V., Jr.
Bibref 1185 - Field Guide to Western Butterflies (Peterson Field Guides) (1999) Opler, P.A. and A.B. Wright

Search More Titles in Bibliography

Additional resources

USDA: Find Ambrosia trifida in USDA Plants
FNA: Find Ambrosia trifida in the Flora of North America (if available)
Google: Search Google for Ambrosia trifida


Record Modified: 2016-01-13
Research By: TWC Staff

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