The effects of sample age and taxonomic origin on the success rate of DNA barcoding when using herbarium material

We have produced DNA barcodes for Finnish plant taxa. In this study, we specifically report the barcoding success for herbarium materials varying widely in age, also paying attention on success rate variation and genetic distances among different plant families. Additionally, we investigated whether the level of intraspecific variation differs between native and introduced species. The specimens had been collected between years 1867 and 2013. Among all studied specimens, the average success rates for any barcode ( mat K or rbc L), rbc L, mat K and both barcodes equaled 81, 79, 55 and 53%, respectively, and among species (at least one specimen per species barcoded successfully) 95, 95, 74 and 73%, respectively. We found significant age effects on the barcoding success, the greatest decline being visible in over 100-year-old samples. Plant families showed differences in overall success rates and sample age effects, as well as in intraspecific and interspecific variation levels, while the average level of intraspecific variation appeared similar among native and introduced species. Besides being valuable for the identification of species, DNA barcoding with sufficient sampling is also a tool to investigate specific evolutionary questions, such as biogeographic patterns or the adaptive capacity of invasive and other alien plant species.