Gene flow can have several different applied consequences, ranging from extinction to the escape of transgenes to the evolution of weedy or invasive lineages. Here, we describe patterns of hybridization and gene flow involving domesticated and wild sunflowers in Argentina. To address the risks of introgression of variants from the cultivated sunflower into invasive wild Helianthus, we used genotyping‐by‐sequencing (GBS) to genotype 182 samples from 11 sites in Argentina, along with previously published data from samples from the native range (North America), to determine the native source populations of the Argentinian samples and to detect admixture. We unexpectedly discovered two distinctive forms of H. petiolaris in Argentina, one from H. petiolaris subsp. petiolaris as expected, but the other from an unknown source. Extensive admixture was observed among Argentinian sunflowers, largely confirming phenotypic predictions. While many hybrids are F1s, there were signals consistent with introgression from the domesticated sunflower into H. petiolaris. Whether this introgression is incidental or a causal driver of invasiveness is not yet clear, but it seems likely that genes found in the domesticated sunflower genome (whether engineered or not) will quickly find their way into wild Argentinian sunflower populations.