A peripatetic overview of milkweed (Asclepias) systematics: phylogeny, diversity, speciation, and hybridization

Milkweeds (Apocynaceae, Asclepias) are iconic perennial herbs in American prairies and deciduous forests, well known for their distinctive flowers that teem with insect pollinators and their pods filled with flossy seeds. Though many people are familiar with 1-2 species of milkweeds, few are aware that there are more than 100 species in North and South America that vary dramatically in stature, the shape and color of flowers, and habitat. These species originated in rapid succession around 20 million years ago in response to a cooling and drying climate that resulted in the extensive grasslands, deciduous forests, deserts, and scrublands of the Americas. In this talk, I will summarize what we’ve learned about the evolutionary history of milkweeds and how they’ve come to be distributed across the continents. I will focus on the ecological contexts of this rapid diversification and how hybridization continues to play a role in milkweed evolution.