The importance of the North Atlantic land bridges and eastern Asia in the post-Boreotropical biogeography of the Northern Hemisphere as revealed from the poison ivy genus (Toxicodendron, Anacardiaceae)

Abstract The Northern Hemisphere was widely covered by a tropical flora (i.e., the Boretropical flora) in the Eocene and the evaluation of plant diversifications in the post-Boreotropical era has become an important challenge to understanding the modern biogeographic complexity in this vast region. Toxicodendron or the poison ivy genus of the sumac family has a temperate to tropical distribution in Asia and North America and can serve as an excellent model for investigating the evolution of the post-Boreotropical biogeographic complexity. Molecular age estimates were calculated using a Bayesian approach with sampling covering the taxonomic diversity and biogeographic distributions within the genus, and sequence data from three nuclear DNA (ITS, ETS, NIA-i3 ) and two chloroplast ( ndhF , trnL-F ) regions, combined with calibrations from three fossil records. Ancestral areas were reconstructed using RASP and BioGeoBears. Toxicodendron is estimated to have a Boreotropical origin in the New World in the late Eocene at 37.68 Ma. It then diversified into a subtropical-temperate and a tropical lineage, followed by migrating into eastern Asia via the North Atlantic land bridges in the Oligocene to early Miocene. Two tropical migration events during the Miocene are identified between continental Asia and SE Asia or New Guinea around 20.91 Ma and 14.33 Ma, respectively. Results from this study highlight the importance of the North Atlantic land bridges and eastern Asia in the post-Boreotopical plant divergences in the Northern Hemisphere, especially when biogeographic exchanges between North and South America were limited.