Invasion of Ambrosia artemisiifolia in Italy: Assessment via analysis of genetic variability and herbarium data

Ambrosia artemisiifolia Italian populations (HE = 0.687) had higher values of genetic diversity when compared to Canadian (HE = 0.639) and French (HE = 0.643) populations. Nevertheless, the time of residence of the Italian populations was positively correlated with the observed and expected heterozygosity (HO, HE). Genetic clustering inferred in STRUCTURE suggested admixture of populations with different ancestry. Historical distributional data highlighted that A. artemisiifolia first colonised the Po plain and different phased localities of the Mediterranean region. This study synthesises genetic and historical distributional data, highlighting that several invasion events have occurred across the Italian peninsula in different spatio-temporal steps, establishing high levels of historic gene flow between populations with mixed ancestry.