Cladotypic Taxonomy Revisited

New propositions are made in order to implement the cladotypic taxonomic system. The term ‘taxon’ designates metapopulation lineages that evolved from a unique metapopulation lineage. In other words, a taxon is composed of a species that experienced a cladogenesis event, and all its descendants. A new formulation for the defi nition of particular taxa is proposed: a taxon is a species that evolved from the (segments of) metapopulation lineage in which the character state [defi ning character state], as exhibited by [species 1] and [species 2], has been acquired. An assumption on the polarity of type character states is developed in order to allow the falsifi cation of taxa defi ned by symplesiomorphies. It is based on a new sense given to ‘adelphospecies’ (or adelpholineage) and to the new concept of ‘amitaspecies’ (or amitalineage). The adelphospecies is understood as the closest sister-species of a taxon T to which the character involved in the defi nition of T is applicable. As a consequence of the defi nition of T, the adelphospecies exhibits a character state different from that exhibited by T. The amitaspecies is the closest sister-species of the taxon including T and its adelphospecies. The assumption of polarity takes the form: an amitaspecies can be identifi ed and, regarding the character involved in the defi nition, it exhibits a character state different from that exhibited by the taxon. Finally a practical version of the isolation assumption is proposed.