Several problems of the polyphasic approach in the modern cyanobacterial system

The taxonomic criteria for cyanobacteria were substantially changed with the introduction of electron microscopy and molecular analyses. The system must be modified according to the results following from these studies and the genetic diversification in various clades must be used as an obligatory basic method for cyanobacterial classification. However, cytomorphological and ecological data cannot be neglected. It is necessary to discover always the relations, correlations, interactions, and coincidences between the genetic basis and morphological and ecological markers. They can have various taxonomic values in various clades and their importance must be re-evaluated in different taxa, but they cannot be omitted. Therefore, cryptic, morpho-, and ecospecies also appear based on different kinds and combinations of characters. The polyphasic approach is a methodological procedure that has been a means of dealing with all these problems. From this approach, the modern cyanobacterial system resulted in which numerous genera were divided into more generic entities, as well as making problematic the use of some traditional expressive characters, such as unicellularity vs. filamentous forms, the presence of sheaths, type of branching, presence of aerotopes, etc. The nomenclatural rules for phototrophic organisms must be respected even in this new system.