DNA barcodes from four loci provide poor resolution of taxonomic groups in the genus Crataegus

The leaves and fruits of some of the approximately 230 species of hawthorn (Crataegus) yield natural health products with significant therapeutic effects on symptoms of cardiovascular disease. DNA barcoding could be a valuable tool for authenticating these products. However, in a new study published in AoB PLANTS, only a small fraction of the 93 taxa examined by Zarrei et al. were distinguished, even though all major clades and eight out of ten taxonomic sections of the genus were included. DNA barcoding as currently practised thus has limited utility in Crataegus. Hybridization, lineage sorting due to incomplete concerted evolution in ITS2, and limited variation in plastid loci are implicated.