Pursuit of a natural classification of diatoms: History, monophyly and the rejection of paraphyletic taxa

Diatom classification is changing. We briefly discuss the history of diatom classification and comment on some of the most recent systems derived from the analysis of molecular data. Classification is not about “sources” of data, but the recognition of monophyletic groups based on evidence. We note that through recent history, with observations based on light microscopy, electron microscopy and molecular analysis, the creation of paraphyletic groups and their retention has been the tradition, leaving a natural classification of the group wanting. Replacing one paraphyletic system with another is a pointless exercise in authority. Congruence between phylogenetic analysis and classification may yield a dramatic restructuring of the classification of the diatoms, and that has implications for training future diatom researchers.