On 9 May 2024, Michael Simpson gave a talk for the California Botanical Society, entitled “Dispersal between American Continents and the Special Case of Popcorn Flowers.” This talk reviews American Amphitropical Disjunctions (AADs), plants found in both North and South America on either side of the tropics. Topics covered include mechanism, timing, and direction of long-distance dispersal, correlation with major world bioregions, and changes in plant duration, polyploidy, and reproductive biology following dispersal to the recipient continent. Collections of many of these plant species are deposited in the SDSU Herbarium of our Biodiversity Museum.