1. By increasing vigour and broadening ecological tolerances, hybridization between native and introduced species may serve as a primary driver of invasiveness.
2. Cattails (Typha, Typhaceae) are clonal wetland graminoids that are known to hybridize where anthropogenic influences have resulted in distributional overlap.
3. In order to gauge the relative performance of hybrid vs. pure Typha, we characterized hybridization and clonal growth where native Typha latifolia and introduced Typha angustifolia occur together in the Western Great Lakes Region of North America.
4. Based on microsatellite markers, we documented F1 hybrids as the most common class at five intensively sampled sites, constituting up to 90% of the genets and 99% of the ramets. Backcrosses to one or the other parent constituted 5–38% of the genets. Pure T. latifolia was rare and never constituted more than 12% of the genets.
5. F1 hybrid genets achieved the highest mean ramet numbers at three sites, and were second in size only to T. angustifolia at two sites; however, these differences were not significant based on site-specific one-way anovas.
6. F1 hybrids exhibited little height advantage over other Typha classes, although there was a general tendency for hybrids in relatively mixed stands to be among the tallest genets in shallow water, but among the shortest genets in deeper water.
7. Native T. latifolia was found growing at the shallowest water depths at the only site where it was sufficiently abundant to be included in statistical comparisons.
8. Synthesis. The role of hybridization in plant invasions can be difficult to confirm in the absence of molecular data, particularly for clonal species where the boundaries separating individuals are otherwise difficult to discern. Here, we used molecular markers to document the prevalence and performance of hybrid genets in five invasive Typha stands covering a broad area of the Western Great Lakes Region. We found an extremely high prevalence of F1 hybrids within mixed Typha stands. This, coupled with the typically larger sizes of hybrid genets, suggests that hybrids are capable of outperforming other Typha spp. and that hybridization has played an influential role in the North American cattail invasion.