Phenology data for watermilfoil taxa Myriophyllum spicatum, M. sibiricum, and M. spicatum x M. sibiricum in Minnesota, USA, 2017 - 2018 Glisson, Wesley J; Larkin, Daniel J (2021)

In North America, the hybrid aquatic plant Myriophyllum spicatum × Myriophyllum sibiricum (hybrid watermilfoil, HWM) is a cross between non-native invasive Eurasian watermilfoil (M. spicatum, EWM) and native northern watermilfoil (M. sibiricum, NWM). We compared HWM to its parental taxa, EWM and NWM, by examining the amount and timing of: 1) flowering, 2) surface cover, and 3) biomass (using stem counts as a proxy). We conducted repeat surveys of Myriophyllum beds at eight lakes (2–3 lakes/taxon) in the Minneapolis-St. Paul Metropolitan area (Minnesota, USA) between June 2017 and November 2018. To sample biomass without destroying plants, we developed a novel sampling device that uses underwater video to measure Myriophyllum stems; we validated the utility of this device by comparing Myriophyllum stem counts and biomass collected from the same locations. The data from these studies are provided and documented here.