[Cal-IPC] Origins: Ambrosia trifida (giant ragweed) is native to the central and eastern United States. (link added by Jessica Johnston)

[CDFA] Introduction: Worldwide Distribution: Native to eastern North America. Giant ragweed has been introduced to, and is now established in western North America and much of Asia and Europe. Official Control: Giant ragweed is listed as a noxious weed in at least three states (California, Delaware, and Illinois). California Distribution: Giant ragweed has been reported in 10 California counties (Contra Costa, Glenn, Orange, Los Angeles, Madera, Monterey, San Diego, San Joaquin, San Luis Obispo, and Siskiyou). Most of these records are from residential gardens. According to one source, it is not naturalized in California, but occurs as a waif and/or garden escape. California Interceptions: Recent collections from 2011 through 2014 originated from gardens or as seed contaminants intercepted at the CA border. It is commonly intercepted in feed seed shipments entering the state. (link added by Jessica Johnston)