What is Ragweed?
{{automatic taxobox |name = Ragweed |image = Ambrosia psilostachya kz1.jpg |image_caption = ''Ambrosia psilostachya'' |display_parents = 3 |taxon = Ambrosia |authority = [[Carl Linnaeus|L.]] |synonyms = *''Acanthambrosia'' <small>Rydb.</small> *''Franseria'' <small>Cav.</small> *''Hymenoclea'' <small>Torr. & A.Gray ex Torr. & A.Gray</small> *''Xanthidium'' <small>Delpino</small> *''Gaertneria'' <small>Medik.</small> *''Hemiambrosia'' <small>Delpino</small> *''Hemixanthidium'' <small>Delpino</small> |synonyms_ref = <ref>{{cite web |url=http://dixon.iplantcollaborative.org/CompositaeWeb/default.aspx?Page=NameDetails&TabNum=0&NameId=3bbd95d1-9e99-4636-83c3-70a7aeb9755d |title=Global Compositae Checklist |access-date=6 March 2015 |archive-date=9 March 2015 |archive-url=https://archive.today/20150309135511/http://dixon.iplantcollaborative.org/CompositaeWeb/default.aspx?Page=NameDetails&TabNum=0&NameId=3bbd95d1-9e99-4636-83c3-70a7aeb9755d |url-status=dead }}</ref> }} '''Ragweeds''' are [[flowering plants]] in the [[genus]] '''''Ambrosia''''' in the family [[Asteraceae]]. The most widespread species of the flower in North America is ''Ambrosia artemisiifolia''.There are over 40 species. Most of them occur in the [[southwestern United States]] and northwestern [[Mexico]].<ref name=leon>{{cite journal |first1=José Luis |last1=León de la Luz |first2=Jon P. |last2=Rebman |date=June 2010 |title=A new Ambrosia (Asteraceae) from the Baja California Peninsula, Mexico |journal=Boletín de la Sociedad Botánica de México |volume=86 |issue=6 |pages=65–70 |url=http://www.scielo.org.mx/scielo.php?pid=S0366-21282010000100006&script=sci_abstract&tlng=en}}</ref> Several species have been [[introduced species|introduced]] to the [[Old World]]. Some have naturalized and have become [[invasive species]].<ref name=fna>[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=101325 ''Ambrosia'']. Flora of North America.</ref> Ragweed species are expected to continue spreading across Europe in the near future because of [[climate change]].