Vascular plant diversity in eastern Asia and North America: historical and ecological explanations

Taxonomic diversity of vascular plants (ferns, gymnosperms and angiosperms) was compared between eastern Asia and North America. Eastern Asia has significantly higher species richness in all three classes but the difference was greatest in ferns and least in angiosperms. Differences in taxonomic treatments between the two continents are not likely contributors to these patterns. The relationship of regional to global species richness across the three plant classes suggested that diversity patterns were relatively homogeneous at three taxonomic levels. Thus, differences in species richness are established at the family level and are therefore relatively old. The previously noted fact that eastern Asia has a higher proportion of primitive taxa was shown by analyses both among and within plant classes. Diversity patterns across three taxonomic levels (i.e. family, genus and species) of the three classes may reflect the relative historical positions of the two continents (following continental drift) to the centre(s) of their origin, neighbouring land masses, differential speciation/extinction rates, and switches in dominance levels associated with climate change (including glaciation), as well as reproductive/dispersal mechanisms of the three plant classes.