Phylogenetic analysis places Spicaticribra within Cyclotella

Abstract

A strong consensus has emerged that taxonomic classifications should be based on an underlying phylogenetic hypothesis. According to this view, named groups should be monophyletic, ensuring that a name uniquely matches the evolutionary history and biological attributes of a group of taxa. As originally conceived, the diatom genus Cyclotella is a large and morphologically diverse assemblage of taxa that we now know consists of several distantly related lineages. Considerable progress has been made in placing these lineages into different monophyletic genera. The genus Spicaticribra was originally described as monotypic and has features that suggest a close relationship to Cyclotella, but it has also retained some ancestral features that appear to differentiate it from Cyclotella. We sequenced two nuclear and two plastid genes to resolve the phylogenetic position of Spicaticribra and show that it is embedded within a clade that includes the type species of Cyclotella and, further, that maintaining Spicaticribra renders Cyclotella non-monophyletic. We transfer Spicaticribra species into Cyclotella, resolve related nomenclatural issues, and caution against using ancestral characters and character states for taxonomic classification.