The effect of purple loosestrife (Lythrum salicaria L.; Lythraceae) on the pollination and reproductive success of sympatric co-flowering wetland plants

Abstract

This study investigated the effect of purple loosestrife (Lythrum salicaria L.) on the pollination and reproductive success of co-flowering plant species (Impatiens capensis Walt., Eupatorium perfoliatum L. and Eupatorium maculatum L.). Pollinator visits, heterospecific and conspecific stigmatic pollen loads, fruit and seed set were measured and compared among experimental plots of low, medium, and high densities of Lythrum salicaria. Honey bees accounted for over 90% of the visits to Lythrum salicaria. In medium-density plots, in one of the two study sites, there was 19% reduction in seed production in Eupatorium perfoliatum and more than 58% increase in the amount of Lythrum salicaria pollen on Eupatorium maculatum stigmas. In high-density plots, at one site, 30% fewer fruit set in Impatiens capensis. These data indicate that Lythrum salicaria can have a negative impact on wetland plant communities.