The nuclear internal transcribed spacer (ITS2) as a practical plant DNA barcode for herbal medicines

• Herbal products (HMPs) from New York City were DNA barcoded for rbcl, matK and ITS2.
• We found that ITS2 was easier to amplify and can discriminate species on its own.
• We were more successful in barcoding leaf and root HMPs than barks.
• 4 of 47 herbal products barcoded did not contain the species declared on the label.
• ITS2 DNA barcoding is a practical tool to authenticate herbal products.

With the development of DNA barcoding methods and databases, misidentification may be easily caught. However, this technique has presented challenges with regard to the tissue type and marker locus variation. In this study, DNA barcoding was used to investigate the taxonomic accuracy of herbal medicines sold in the New York City (NYC) area using the plastid markers rbcL, matK and the nuclear ribosomal region ITS2. Forty-seven (47) samples (single-ingredient herbal medicinal products or HMPs) were purchased from eight herbal stores, and represented different structures: 22 leaf samples, 11 roots, 9 barks, and 5 samples that were ground beyond recognition. MEGABLAST sequence comparison was performed to verify the taxonomic identity of the samples. Maximum likelihood trees were constructed for sequence queries with equivocal multiple high-scoring MEGABLAST hits. Of the barcodes, ITS2 had the most success being amplified and sequenced (barcoded) in 38 of the 47 HMPs (81%), mostly leaf and root samples as barks were difficult to barcode. This is in contrast to 26/47 (55%) and 15/47 (32%) successful barcoding for rbcL and matK, respectively. ITS2 alone was accurate enough to match 88% of ITS2 sequences to the expected species, while only 59% of sequenced rbcL and 45% of matK was able to match with the expected species. All four HMPs obtained from one store did not match the declared species on the label based on ITS2, and this result was echoed by the rbcL and matK barcodes. However, all other herbal stores appeared to be selling accurately labeled HMPs. Our study showed that DNA barcoding is a worthwhile effort to test HMP authenticity, which may help build reputation of quality brands and ensure consumer safety. ITS2 is a practical DNA barcode that regulatory agencies may propose to NYC herbal medicine manufacturers and merchants to ensure quality.