Freezing tolerance of seeds can explain differences in the distribution of two widespread mistletoe subspecies in Europe

•Lethal temperature (LT50) of seeds of European mistletoes varied between −15 °C and −19 °C.•Seeds of Viscum a. album tolerated lower temperatures than seeds of V. a. austriacum.•Potential distribution of European mistletoes will move northwards due to climate warming.•Mistletoes will increase in abundance at their current northern limit.