Biogeographical patterns of plants in the Neotropics – dispersal rather than plate tectonics is most explanatory


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The phylogenetic relationships of some Neotropical plant groups have proved to be different from expectation assuming plate tectonics as the underlying model, and these unanticipated relationships (and their timing) have required further work to explain how they came into existence. Well-known Neotropical families, such as Bromeliaceae and Cactaceae, have one to a few species in Africa, but these can be explained by recent long-distance dispersals; the estimated ages of the Transatlantic crown and stem clades of these families are of relatively recent origin, so long-distance dispersal is the only possible explanation and plate tectonic explanations are not viable. Other families with a crown age appropriate to be explained by plate tectonics did not seem to have distributions indicating an involvement of long-distance dispersal, but the advent of molecular systematics and molecular clocks has shown this to be otherwise. Families exhibiting this pattern include Fabaceae and Lauraceae (and many others), and in spite of the unlikely dispersal qualities of their generally large seeds, they exhibit many instances of long-distance dispersal occurring throughout their evolutionary history; in fact, long-distance dispersal is the most probable explanation to account for the current distributions of the great majority of land plant families. One factor that sometimes is overlooked is the boreotropics hypothesis, which may explain more recent connections between American, African and Asian floristic components. However, in some old lineages with small propagules that appear well adapted to long-distance dispersal, such as Marattiaceae and Orchidaceae, we find a pattern suggesting that tectonics is the primary factor, with clades clearly restricted to one tropical region. These patterns appear to have little to do with dispersability and it is probable that their conforming to expected (tectonic) biogeographical patterns has to do with their specialized life-history strategies that have acted to make intercontinental establishment unlikely even though dispersal almost certainly occurs. Molecular studies have identified additional, unanticipated clades, and these fit into the relictual category with what may be an overlay of old long-distance dispersal events. Examples at the ordinal level are Crossosomatales and Huerteales, and we expect future studies to identify more of these relict and unexpected clades at many taxonomic levels. Overall, molecular systematic studies and molecular clocks have demonstrated that there are many more connections between the Neotropics and Palaeotropics, both Asia and Africa, than previously would have been thought under a plate tectonic model. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012,●●, ●●–●●.