Reproductive mode and mating system in the invasive wintercreeper vine ( <i>Euonymus fortunei</i> ) in southwestern Ohio: polyembryony, apomixis, selfing, and outcrossing

Abstract Spread of invasive species can be impacted by their mode of reproduction (asexual vs. sexual) as well as the mating system (outcrossing vs. selfing). This is especially the case in the evergreen wintercreeper vine [ Euonymus fortunei (Turcz.) Hand.-Maz.], which was originally brought to the United States for horticultural purposes and is now considered invasive across the Midwest. Wild wintercreeper populations consist primarily of a single polyploid genotype, the ornamental ‘Coloratus’ cultivar, but it is still unknown how this species produces its fruit during the fall. We examined the reproductive mode and mating system of wintercreeper by collecting leaves and fruits from 12 wild plants in an urban location of Cincinnati, OH. In this genetic survey, we used microsatellite markers to identify the pollen donor of each embryo within the seeds. Polyembryony was relatively common, with 37.4% of seeds each containing two to four embryos. Many of the 382 embryos extracted were produced asexually through apomixis (50.0%) or were sexual products of outcross fertilization (34.3%) or self-fertilization (15.7%). In seeds with multiple embryos, larger embryos were most likely to be outcrossed, with winged burning bush [ Euonymus alatus (Thunb.) Siebold ‘Compactus’] as the most likely pollen donor, and apomixis increasing in successively smaller embryos. Single embryos within seeds were more often outcross fertilized (52%). The fact that all wild adult wintercreeper plants consist of a single genotype is consistent with the production of these apomictic offspring. However, lack of sexually produced wild plants, despite their appearance in the embryonic stage, warrants further study. This is the first report of polygamous apomixis in this species, and research is continuing into how this reproductive strategy may influence invasive spread of the species.