Dual nomenclature to be supported explicitly in the International Code of Nomenclature for algae, fungi, and plants

Dual nomenclature as applied to dinoflagellates is underpinned by conceptual and practical considerations. It allows the separate naming of fossil- and non-fossil species even when they are linked to one another by incubation studies and other techniques. It is needed because fossil- and non-fossil taxonomies are based on different stages of the life cycle and cannot be integrated at the generic level. All taxonomists today who study dinoflagellates, whether living or fossil, place their work under the International Code of Nomenclature for algae, fungi, and plants. The Shenzhen Code and its predecessors have supported dual nomenclature implicitly with the help of examples, but without clear explanation of what it is and how it works. In Madrid, Spain, in July 2024, the Nomenclature Section of the XX International Botanical Congress approved two new articles for the Code that remove earlier contradictions and introduce dual nomenclature explicitly, drawing on a critical distinction between ‘synonymy’ and the new concept and term ‘taxonomic equivalence’. These changes will be incorporated into the forthcoming Madrid Code. In addition to placing the Code in its historical context, we explain how it is amended in order to demystify an intricate but important procedure.