What Is a Taxon? Identity, Persistence, and Operability in Taxonomy

Although central reference units in biology, taxa remain difficult to integrate coherently across scientific and digital frameworks because they are repeatedly created, destroyed, or redefined through taxonomic revisions. To address this problem, we develop a conceptual and ontological analysis of taxonomic practice that distinguishes taxa from biological lineages, phylogenetic clades, names, and individual taxonomic treatments. We show that a taxon is a historically continuous object of knowledge instituted by a formal taxonomic act, whose identity is carried by a taxonomic temporal string, whose changing content is its taxonomic substance, and whose published interpretative history is its taxonomic trajectory. This framework is constrained by empirical properties of taxonomic practice, including persistence, historical continuity, irreversibility, revisability without destruction, traceability, and variable operability through time. Within this model, splitting, lumping, synonymy, and redefinition are interpreted as redistributions or reconfigurations of taxonomic substance rather than the creation or destruction of taxon identities. The framework also clarifies the articulation between taxonomy, phylogeny, and biological data by separating stable reference objects from the hypotheses that inform them. Because taxa originate only through unique code-compliant formal acts, they are intrinsically suitable for persistent identifiers (PIDs), enabling unambiguous and interoperable digital integration of systematic knowledge for biodiversity.