Molecular Plant Taxonomy

Weston PH, Peter H. Weston, Weston, Peter H.

Molecular systematics has revolutionized our understanding of the evolution of the Proteaceae. Phylogenetic relationships have been reconstructed down to generic level and below from alignments of chloroplast and nuclear DNA sequences. These trees have enabled the monophyly of all subfamilies, tribes, and subtribes to be rigorously tested and the construction of a new classification of the family at these ranks. Molecular data have also played a major part in testing the monophyly of genera and infrageneric taxa, some of which have been recircumscribed as a result. Molecular trees and chronograms have been used to test numerous previously postulated biogeographic and evolutionary hypotheses, some of which have been modified or abandoned as a result. Hypotheses that have been supported by molecular phylogenetic trees and chronograms include the following: that the proteaceous pattern of repeated disjunct distributions across the southern hemisphere is partly the result of long-distance dispersal; that high proteaceous diversity in south-western Australia and the Cape Floristic Region of South Africa is due to high diversification rates in some clades but is not an evolutionary response to Mediterranean climates; that the sclerophyllous leaves of many shrubby members of the family are not adaptations to dry environments but for protecting mesophyll in brightly illuminated habitats; that deeply encrypted foliar stomata are adaptations for minimizing water loss in dry environments; and that Protea originated in the Cape Floristic Region of South Africa and that one of its subclades has greatly expanded its distribution into tropical savannas. Reconstructing phylogeny down to species level is now the main goal of molecular systematists of the Proteaceae. The biggest challenge in achieving this task will be resolving species trees from numerous gene trees in complexes of closely related species.