The new systematics of scleractinia: Integrating molecular and morphological evidence

The taxonomy of scleractinian corals has traditionally been established based on morphology at the “macro” scale since the time of Carl Linnaeus. Taxa described using macromorphology are useful for classifying the myriad of growth forms, yet new molecular and small-scale morphological data have challenged the natural historicity of many familiar groups, motivating multiple revisions at every taxonomic level. In this synthesis of scleractinian phylogenetics and systematics, we present the most current state of affairs in the field covering both zooxanthellate and azooxanthellate taxa, focusing on the progress of our phylogenetic understanding of this ecologically-significant clade, which today is supported by rich sets of molecular and morphological data. It is worth noting that when DNA sequence data was first used to investigate coral evolution in the 1990s, there was no concerted effort to use phylogenetic information to delineate problematic taxa. In the last decade, however, the incompatibility of coral taxonomy with their evolutionary history has become much clearer, as molecular analyses for corals have been improved upon technically and expanded to all major scleractinian clades, shallow and deep. We describe these methodological developments and summarise new taxonomic revisions based on robust inferences of the coral tree of life. Despite these efforts, there are still unresolved sections of the scleractinian phylogeny, resulting in uncertain taxonomy for several taxa. We highlight these and propose a way forward for the taxonomy of corals.