Review of Coral Taxonomy, Evolution and Diversity

Abstract

To recast Theodosius Dobzhansky’s famous 1973 quote: ‘nothing in coral taxonomy makes sense except in light of reticulate evolution’. Coral species evolve through the continual intermixing of ancestral lineages forming a network of changing genetic interconnections rather than stable hierarchical trees. Most species are not discrete units but rather are components of continua with variable genetic, morphological, and geographic boundaries. Hybridisation and introgression are key processes maintaining reticulated networks, making polyphyletic species (those with mixed evolutionary origins) potentially the norm. This creates grey zones of speciation where taxonomic divisions are uncertain and gene flow is ongoing. With this understanding, we critically review: (1) Sources of information for taxonomic decisions, including biology, population dynamics and the need for comprehensive field and foundational molecular studies capturing environment-correlated and geographic variations; (2) Nomenclature (a human construct) and taxonomy (which endeavours to reflect nature’s organisation): (3) Synonymy, including serial errors stemming from historical publications; (4) Type specimens, their use and misuse as a basis for taxonomic decisions; (5) Genus and species level agreements and disagreements between morphological and molecular taxonomies; (6) Use of the terms ‘cryptic species’, ‘cryptic variant’ and ‘cryptic lineage’; (7) Taxonomic decisions based on inferences beyond the scope of individual studies, creating nomenclatural instability and concern, not least among those working to address the impacts of climate change. This review also provides context for an extensive array of Factsheets and linked documentation about each of the species included in CoralsOfTheWorld.org (2026 in prep.).