One possible explanation for this
apparent contrast between plant and animal distributions is a
difference in the way that plant and animal systematists use the
taxonomic hierarchy. The use of dated molecular phylogenies
removes this potential bias, leaving just two possibilities: either the
major rainforest plant lineages are older than the vertebrate lineages
and could thus achieve pantropical distributions while the major
rainforest land masses were still connected (Box 1), or long-distance
dispersal over water barriers is easier for plants than it is for
vertebrates.