Species, subspecies, and infrasubspecific categories. At
present, the species is the only taxonomic unit that can be
defined in phylogenetic terms. In practice, DNA reassociation
approaches the sequence standard and represents
the best applicable procedure at the present time. The
phylogenetic dejinitibn of u species generally would include
strains with approximately 70% or greater DNA-DNA relatedness
and with 5°C or less AT,. Both values must be
considered. Phenotypic characteristics should agree with
this definition and would be allowed to override the phylogenetic
concept of species only in a few exceptional cases.