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 presented of how both the branching pattern and amount of divergence. both morphological 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 represent evolutionary units held together by aspects of genomic organisation developed over long periods of time. Radiations that produced extant lineages (families) only became successful (as measured by taxon-richness) after more of the genomes of these plants were recruited into highly canalised syndromes of characteristics. Thus, single evolutionary novelties are less important 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 led to the incorporation of divergence into classification. Using DNA patterns as a general meter of overall generic divergence provides another means of evaluating family delimitation in groups that are not apparently as morphologically 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 with a multi-purpose classification, the delimitation of some highly heterogeneous taxa is inevitable.