Higher-level classification in the angiosperms: new insights from the perspective of DNA sequence data

Higher-level classification of the angiosperms has recently been addressed with large amounts of DNA sequence data, and this wealth of information now facilitates a wide range of other studies as well. An overview is presente d of how both the branching pattern and amount of divergence. both morpholo gical and molecular, can be applied to familial and ordinal classification. Angiosperm families have been classified as easily with DNA sequence data as they had been previously with morphological characteristics and represen t evolutionary units held together by aspects of genomic organisation devel oped over long periods of time. Radiations that produced extant lineages (f amilies) only became successful (as measured by taxon-richness) after more of the genomes of these plants were recruited into highly canalised syndrom es of characteristics. Thus, single evolutionary novelties are less importa nt in the context of the long histories of these families than is otherwise generally held for recent species/generic radiations. After monophyly, the secondary principles of maximising both information content and support le d to the incorporation of divergence into classification. Using DNA pattern s as a general meter of overall generic divergence provides another means o f evaluating family delimitation in groups that are not apparently as morph ologically cohesive as most, although circumscribing families based on such patterns will inevitably lead to taxa that cannot be readily identified in the field. Nonetheless, in the interests of providing other researchers wi th a multi-purpose classification, the delimitation of some highly heteroge neous taxa is inevitable.