DNA sequencing identification methods are often referred to collectively as "DNA barcoding", and use one or several short DNA sequences to identify organisms. For plants the two generally used DNA barcode regions are the rbcL and matK genes, located in the chloroplast genome; although these two regions are often supplemented by additional DNA barcode regions, such as the Internal Transcribed Spacers (ITS) of the nuclear ribosomal DNA. DNA barcoding provides an alternative identification approach to traditional morphological methods, with the advantage that DNA can usually be obtained from any part of an organism including leaves, roots, stems, seeds or even pollen.
Before DNA barcoding can be undertaken, it is crucial to build a reference library of DNA sequences, obtained from plant specimens (known as vouchers), stored in a herbarium where they have been identified by taxonomic botanists. It is valuable to have multiple samples from each species, ideally from across their natural range, to account for potential intraspecific variation. These reference samples allow species identification to be linked to a verifiable herbarium record, which can be checked if the molecular information is in conflict with expectations based on morphology, or if there is a need to obtain further data.