A bstract: The three-taxon statement is the fundamental unit of rooted trees in Cladistics, stating that for three terminal taxa, two are more related to each other than to a third. Because of their fundamental role in phylogenetics, three-taxon statements are present in methodological research of various disciplines in evolutionary biology, as in consensus methods, supertree methods, species-tree methods, distance metrics, and even phylogenetic reconstruction. However, three-taxon statements methods are subject to important flaws related to information redundancy. We aim to study the behavior of three-taxon statements and the interactions among them in order to enhance their performance in evolutionary studies. We show here how specific interactions between three-taxon statements are responsible of the emergence of redundancy and dependency within trees, and how they can be used for the improvement of weighting procedures. Our proposal is subsequently empirically tested in the supertree framework using simulations. We show that three-taxon statements using fractional weights perform drastically better than classical methods such as MRP or methods using unweighted statements. Our study shows that appropriate fractional weighting of three taxon statements is of critical importance for removing redundancy in any method using three-taxon statements, as in consensus, supertrees, distance metrics, and phylogenetic or biogeographic analyses.

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.