Assessing Ecological Impacts of Cultivated Hybrids of Milkweed (Asclepias)

Abstract Increased efforts to use native plants to provide ecosystem services in urban landscapes have led to breeding efforts to increase access to native plants in horticulture markets. Inadvertent ecological impacts however should be assessed prior to market release. Here we trial new interspecific hybrids of milkweed to assess outcrossing into natural populations and support for pollinating species. Interspecific hybrids of Asclepias were unable to successfully fertilize A. tuberosa, indicating minimal likelihood of outcrossing into natural populations. Hybrids lacked self-fertilization and the ability to cross with full-siblings, indicating low levels of establishment of the interspecific hybrids into natural environments. Nectar composition and nectar concentration were similar among hybrids and A. tuberosa, revealing there was not a loss in floral rewards, despite trait selection for horticulturally preferable traits. Pollinator abundance was higher on hybrids than on A. tuberosa, and richness and diversity of pollinator species were similar among hybrids and A. tuberosa, indicating that the hybrids can offer similar or more ecosystem services as A. tuberosa. New interspecific hybrids of Asclepias selected for horticulturally preferable traits have shown ecological value similar to A. tuberosa with respect to supporting pollinating species and minimal ecosystem impact for natural populations of A. tuberosa. Species used in this study: butterfly weed (Asclepias tuberosa L.); tall green milkweed [Asclepias hirtella (Pennell) Woodson]; common milkweed (Asclepias syriaca L.); showy milkweed (Asclepias speciosa Torr.); purple milkweed (Asclepias purpurascens L.); Asclepias tuberosa × hirtella; Asclepias tuberosa × syriaca; Asclepias tuberosa × speciosa; Asclepias tuberosa × purpurascens.