A phylogenetic classification of diatoms (Bacillariophyta)

Diatoms are known for their extraordinary species richness, cornerstone roles in aquatic ecosystems, and immense contributions to the global cycling of carbon, oxygen, and silica. For nearly 2 centuries, taxonomic classifications of diatoms have been based on interpretations of their feature-rich, silica cell walls. These classifications, in turn, have been used to make broad inferences about diatom ecology and evolution, but decades of molecular phylogenetic research have shown that historical and contemporary classification systems do not reflect evolutionary history, severely limiting their utility and insights. We took advantage of recent advances in our understanding of the diatom phylogeny to develop the first entirely natural classification of diatoms, in which only monophyletic groups have been recognized and named. The classification is comprehensive, dividing 431 genera among 68 families, 44 orders, and 10 classes. Among these, seven classes, 13 orders, three families, and one genus are proposed as new. Although the new classification includes many areas of overlap with previous systems, one principal departure is the increased number of classes, which reflects that "centric" and "araphid" diatoms are comprised of multiple lineages recognized here as distinct classes. By providing a more accurate representation of phylogenetic relationships, the proposed classification facilitates clearer communication about all aspects of diatom biology.