A DNA sequence does not define a species. DNA varies from individual to individual, and old-fashioned studies of interbreeding populations are still needed in order to determine the range of variation of DNA possessed by that interbreeding population. This means we need some other independent way of determining the limits of an interbreeding population; this can be difficult, especially in plants which are 1) rare and 2) easily form hybrids (including even intergeneric hybrids). I wish DNA barcoding was definitive, but at least in fast-evolving groups of rare plants like the orchids I work with, it is not. Lou Jost