Hybrid watermilfoil (Myriophyllum spicatum × Myriophyllum sibiricum) exhibits traits associated with greater invasiveness than its introduced and native parental taxa

Abstract Hybridization has been associated with increased invasiveness in plants. In North America, the hybrid aquatic plant Myriophyllum spicatum × sibiricum (hybrid watermilfoil, hereafter HWM) is a cross between non-native invasive Eurasian watermilfoil ( M. , EWM) and native northern NWM). Lab-based trials have demonstrated higher growth rates HWM compared to EWM NWM, but these patterns not systematically examined field. this study, we of its parental taxa, by examining amount timing of: (1) flowering, (2) surface cover, (3) biomass (using stem counts as proxy). We conducted repeat surveys beds at eight lakes (2–3 lakes/taxon) Minneapolis–St. Paul Metropolitan area (Minnesota, USA) June 2017 November 2018. produced more flower spikes earlier overall, maintained consistently throughout growing season than NWM. addition, cover reached greater annual peaks was for longer both taxa. did observe significant difference among three reach maximum number stems either taxon. This study provides field-based evidence hybridization NWM; specifically, reproductive potential via flowering may increase spread, impacts on species, pose nuisance lake users.