A Comparison of Generic Endemism of Vascular Plants between East Asia and North America

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Abstract
Biogeographic interpretations sometimes depend on endemism. The diversity of endemic genera of vascular plants in different phylogenetic groups was compared between East Asia and North America. North America has a significantly higher diversity of endemic genera of vascular plants than East Asia (987 vs. 754 genera). However, East Asia holds greater diversity of endemic genera than North America in pteridophytes, gymnosperms, and ranunculids, which are in general evolutionarily old taxa. The two areas do not significantly differ in the numbers of endemic genera in magnoliids and monocots. The overall diversity bias of endemic genera in favor of North America primarily results from caryophyllids, rosids, and asterids, which are relatively advanced lineages. As a result, numbers of endemic genera within phylogenetic groups do not vary in parallel between East Asia and North America. Compared with the world total flora with respect to proportions of numbers of taxa among phylogenetic groups, East Asia and North America both have excesses of endemic genera in asterids and have deficits in magnoliids, monocots, and rosids. The most noticeable differences in diversity of endemic genera between the two continents were found in pteridophytes, gymnosperms, and ranunculids, for which East Asia shows a striking excess compared with the world flora; North America shows a conspicuous deficit in the first two groups with respect to the world flora. Caryophyllids exhibit a reversed pattern with disproportionately more genera in North America and fewer genera in East Asia compared with the world flora. Differences in diversity of endemic genera between the two continents have resulted from different rates of speciation, immigration, and extinction, which have been primarily influenced by land connection, continental drift, geological history, geomorphologic configuration, and climate in the past.