The introduced plant purple loosestrife (Lythrum salicaria) is one of the worst wetland invaders in the northern U.S. and appears to be spreading in Ohio. Gene flow between closely related introduced Lythrum species has been suggested as one possible mechanism of recent spread in purple loosestrife. We have conducted a morphology-based analysis of historical specimens from the OSU Herbarium, and preliminary results are consistent with increasing purple loosestrife hybridization over time. We plan to complement these morphological data with genomic data, using DNA extracted from pollen from a subset of the historical specimens and from new collections made in Ohio. Next Gen sequence data will be analyzed to determine whether morphology-based assessments of hybridization are reliable and to test whether the extent of genetic exchange varies along temporal, spatial or environmental gradients.