Taxonomy needs pluralism, but a controlled and manageable one

Abstract

What we accept as the units to be classified is not just an expression of our current aims and practices but will also impact further classificatory research. The launch of Megataxa invites a dispassionate discussion about the units to be classified and the names associated to them. Specifically, we must address three challenges.—Challenge 1. Living with pluralism in biological classifications. Despite the enormous amount of ink spent on this issue, there is little hope of finding a species concept at the same time satisfactory from a theoretical point of view and reliable as a guide for taxonomic practice. This unavoidably causes a degree of pluralism in biological classification, as the taxonomic units generally described as species are not necessarily comparable. Also, different users of classification may have different expectations, better satisfied by alternative solutions rather than by a consensus classification. The obvious tension between these different expectations cannot be easily solved by authority or consensus, or simply hoping in the future availability of better criteria for species delimitation. - Challenge 2. Managing multiple classifications within one nomenclature system. Changing taxonomy is the source of ambiguity in the meaning of species names. As a consequence, Linnaean names may not be unique and universal labels for the taxa we recognize. The problem can be solved by specifying taxonomic concepts, i.e. by associating the names to the contexts in which these are used.—Challenge 3. Managing the nomenclature for provisionally circumscribed taxa. Molecular Operational Taxonomic Units (MOTUs) do not correspond necessarily to conventional taxonomic species and no simple or universal rule exists to ‘translate’ MOTUs into Linnaean species. Provisionally recognized MOTUs do not get a Linnaean name, but are labelled with a formula, in too many cases following no acknowledged standard and thus becoming useless for communication purposes. Non-Linnaean names, or formulas, for provisionally circumscribed taxa cannot be rejected, but some international consensus is needed.