Assessment of pollination ecology of two understudied native mustards and the potential for interference from invasive garlic mustard

The family Brassicaceae is agriculturally and economically important. However, ecological knowledge gaps persist for some wild species, even in parts of the world that have broadly well-studied flora, like eastern North America. Knowledge gaps for two eastern North American species, Cardamine concatenata and C. diphylla, are concerning for two reasons. First, these species have known associations with rare, specialist insects. Second, the threat posed by the introduction and spread of noxious invasive confamilial garlic mustard (Alliaria petiolata) within their shared native range. Because C. concatenata and C. diphylla have a short phenological window for seasonal development and reproduction they are at increased risk for mutualism disruption via global change pressures. We aim to evaluate the potential for pollination interference by A. petiolata. We compared pollinator visitation and floral phenology in sympatric wild populations of C. concatenata, C. diphylla, and A. petiolata in northeast Ohio. Pollinator counts and morphotype identifications were recorded during in situ pollinator observations. To supplement morphotype identifications, we collected pollinator specimens and identified them to genus or family in the lab. We found overlap in flowering phenology between A. petiolata and C. diphylla. Fourteen pollinator taxa were observed visiting at least one of the focal plant species; of these, seven taxa were recorded visiting all three plant species. Alliaria petiolata is likely disrupting pollination for the native C. diphylla in our sites because flowering phenology overlaps and pollinator taxa are shared. Future studies should focus on range-wide phenological observation and modelling for all three plant species, and pollen load analysis of native plant stigmas in invaded habitats.