Is Myxomycetes (Amoebozoa) a Truly Ambiregnal Group? A Major Issue in Protist Nomenclature.

Myxomycetes is one of the largest groups of protists belonging to Amoebozoa, with ca 1,000 species recognised and more than 4,000 names in use. Historically, myxomycetes were considered fungi or protozoans which, however, fell under the provisions of the former International Code of Botanical Nomenclature (ICBN), currently the International Code of Nomenclature for algae, fungi, and plants (ICN). Attempts to apply the International Code of Zoological Nomenclature (ICZN) to myxomycetes were rare and inconsistent; thus, we argue that Myxomycetes is not a truly ambiregnal group (i.e. one falling under both Codes). Recently, nomenclatural novelties within Myxomycetes have been proposed using ICZN rules, and the application of zoological orthography to myxomycete higher-level taxa in the recent amoebozoan phylogenies is increasingly common. We summarise the consequences of application of either ICN or ICZN to Myxomycetes. In our opinion, nomenclatural stability within Myxomycetes is best served by strict application of ICN. Either treating myxomycetes as falling under ICZN or considering them an ambiregnal group would cause serious nomenclatural instability, mainly owing to the incompatibility of the two Codes as to the date of the starting point of nomenclature and to the appearance of numerous homonyms.