A hitchhiker's guide to modern, practical cyanobacterial taxonomy

There has been an explosion of new Cyanobacterial taxa described within the last two decades. Cyanobacteria exhibit incredible ecological versatility and morphological variability, and thousands of species have already been described using "traditional" approaches (e.g., morphological features). However, DNA sequencing and other molecular tools have provided extensive evidence that the diversity of cyanobacteria is not necessarily congruent with morphology, as many morphological genera (e.g., Phormidium, Leptolyngbya, and Nostoc) are polyphyletic, and species within the genera are often morphologically indistinguishable, thus cryptic. Further confounding systematic assessments, newly erected taxa are often based on a single strain with one or two 16S rRNA gene sequences, may have incomplete formal descriptions, and lack indication of the employed species concepts. Here we have proposed a set of guidelines for cyanobacterial taxonomists. We have focused on the whole process of erecting new taxa: sampling, sequencing (including genomes), phylogenetic inference, phenotype characterization, species concepts, formal descriptions, and codes of nomenclature. Our hope is that these guidelines will help with the laborious but ever-rewarding task of identifying and describing the taxa within the world of cyanobacteria.