Temporal and spatial comparisons of angiosperm diversity between eastern Asia and North America.

Abstract

Abstract Eastern Asia (EA) and North America north of Mexico (NA) have comparable latitude, land area, and climate, but the overall plant diversity is much higher in EA than in NA. Despite intensive studies on disjunct taxa of the two regions, the temporal and spatial diversity patterns between the two floras remain unclear. Here we explore the floristic differences between EA and NA using the well-studied floras of China and the United States of America (USA) as exemplars, while also employing a newly generated dated phylogeny covering ∼90% of the angiosperm genera of the two countries and comprehensive spatial distribution data. We find that China possesses both higher richness and phylogenetic diversity (PD) for angiosperm genera than the USA. Notably, most lineages contribute to the PD anomaly between the two floras, with 46 of 58 lineages having higher PD in China. Temporally, China has a higher proportion of genera that originated before the Miocene than found in the USA (29.9% vs 23.2%). The eastern USA has more genera that originated during the Paleogene than does the western USA, but the reverse pattern is observed after the middle Miocene, with more genera originating in the west. Spatially, China shows a more distinct east-west deviation in diversity than the USA with eastern China possessing much higher generic richness and PD and more ancient lineages than western China. However, the eastern USA possesses lower generic richness, but higher PD and more ancient lineages than the western USA. Both the floras in China and the USA share a signature of an older east and a younger west, and this pattern may be largely driven by regional orogenic activities and climatic changes in the west of the two regions. Finally, our study indicates that more efforts are needed to enhance biodiversity conservation in southern China and the eastern USA by identifying and protecting phylodiversity hotspots.