[4] Puccinia xanthii is native to the continental United States, Canada, Mexico, Hawaii, Cuba, Haiti, the Dominican Republic, Puerto Rico, and the Bahamas.

[5][3] This fungus has been reported in several countries throughout Europe, Asia, Africa and Australia; often following the introduction of invasive host plants from North America or intentional release as a biocontrol agent.

Researchers have detected P. xanthii in Bulgaria, southern France, Hungary, northern Italy, Romania, Spain, and the former Yugoslavia (Bosnia, Serbia, Slovenia, Montenegro, Macedonia, Herzegovina, and Croatia).

italicum was first found in Beijing, China in 1991 and has been shown to decrease the biodiversity of native flora and cause human health hazards from allergenic pollen.

[11] Puccinia xanthii was found growing on Helianthus annous in the Northwest Province of South Africa in February 2000.

[12] Puccinia xanthii is a rust in the phylum Basidiomycota, subphylum Pucciniomycotina, class Pucciniomycetes, order Pucciniales, and family Pucciniaceae.

[2] Its full scientific name is Puccinia xanthii Schwein., Schriften der Naturforschenden Gesellschaft zu Leipzig 1:73.

[13] Using data from ITS (internal transcribed spacer) and TEF (translation elongation factor) phylogenetic analyses, the closest relative of P. xanthii is P. melampodii, and these species are a sister group to the fungus Dietelia portoricensis.

al proposed that P. xanthii, P. melampodii, and 51 other microcyclic rusts from the Americas and Eurasia that infect members of the Asteraceae should be grouped under the single morphospecies name Puccinia cnici-oleracei.

[14] This complex is based on morphology and needs further proof to be considered valid, however, P. xanthii and P. melampodii could not be easily separated at the species level using phylogenetic data from the ITS and TEF regions.

This high level of genetic variation is created through sexual recombination during karyogamy, somatic hybridization, mutations, and genes introduced from closely related species or other strains of P.

[3] Outside of its native range, this North American weed has caused issues in agriculture via allopathic chemicals, decreased biodiversity, and its pollen is a human health hazard.

[1][6] This means that it only produces basidiospores and teliospores (and lacks spermatia, aeciospores, and urediniospores) and completes its life cycle on a single living host plant.

[1] The penetration peg continues growing and forms intraepidermal vesicles to contain the remaining contents of the basidiospore before putting down a septum and differentiating into primary hyphae.

[1] Puccinia xanthii will form dark brown telia in a thallus that erupts through the leaf surface seven to eight days after inoculation.

[5][18] These telia will bore teliospores that can either germinate immediately if conditions are favorable or act as a survival structure for the fungus.

Puccinia xanthii forms dark brown pustules (raised spots) with a chlorotic halo on the adaxial, and sometimes abaxial leaf surface.

[5][4] In the early stage of infection, P. xanthii causes yellow lesions that gradually turn brown in the center as telia are produced.

Kassai-Jager et al. has also recommended the use of this pathogen as a classical biocontrol agent in Australia against another invasive member of the Asteraceae from North America, Ambrosia artemisifolia.

Puccinia xanthii could infect and cause foliar damage to Helianthus annus and Calendula offiinalis in pathogenicity tests using strains from C. officinalis in Queensland.