Ability of Impatiens seed to float increases invasion success
Both Impatiens glandulifera (EPPO List of Invasive Alien plants) and I. balfourii (Balsaminaceae) were introduced into the EPPO region from the Western Himalayas as garden ornamentals. Since then, they have both spread within the region though I. glandulifera is by far the more successful invader. In the EPPO region, both species sometimes grow near to rivers, and upon maturity seed can become incorporated into the water body and moved with the flow of water. The floating ability of seeds of the two Impatiens species were tested following seed field collections from young and old populations of both species in September/October. Floating ability was determined under controlled conditions and both still water conditions and moving water conditions were tested. Seeds of I. balfourii floated less well than seeds of I. glandulifera. Seeds of I. balfourii from the younger population have a higher floating ability compared to seeds from the older population. The results for I. glandulifera were the opposite, with decreased floating ability in the younger population. These differences were associated with seed surface, shape and coat structure. The results suggest that the floating ability of I. balfourii seeds may increase over time following its introduction into a given area, while in the case of I. glandulifera, this ability may gradually decrease. The ability of seeds to float may promote the invasiveness of alien plant species. I. balfourii may have undergone changes in terms of the floating ability of its seeds and therefore although it is commonly regarded as a poor disperser, its lag phase maybe coming to an end. Consequently, the rate of its spread may significantly increase, and it may become a truly invasive alien species in Europe.
Sources
Najberek K, Olejniczak P, Berent K, Gąsienica-Staszeczek M, Solarz W (2020) The ability of seeds to float within water currents contributes to the invasion success of Impatiens balfourii and I. glandulifera. Journal of Plant Research 133, 649-664.