Plant-based natural products research is conducted using a wide variety of source material. The plant material is often obtained directly from the wild, from cultivated plants originally obtained from the wild, or purchased in raw or processed forms. In plant science a voucher specimen usually consists of a pressed, dried herbarium specimen with detailed collection data and serves as a record of an individual plant in time and space. This review article describes why vouchering is necessary and documents actual examples of how improper vouchering can result in serious problems. The primary reason for vouchering is to have a permanent record documenting the material that was used in a particular study. If a specimen is not saved or is not made available to others, the true identity of the plant materials used in a research project may be questioned. Due to the morphological and chemical complexities of interspecific hybrids, within-species variation, and the difficulty associated with identifying species in certain plant genera, the preservation of vouchers is essential for the documentation of the identity and source of such plant material. The use of best practices in specimen preparation is critical for successful documentation. The lack of proper voucher specimens for some research projects has led to serious problems, such as the inability to reproduce critical results, the association of chemical data with the wrong genus and species, and even the complete rejection of the published research results. In cases where plant material was initially misidentified and properly prepared voucher specimens were available, the identities of the research material were eventually corrected and the data was subsequently associated with the correct species, retaining the inherent scientific value of the research.
Eisenman, Sasha W.; Arthur O. Tucker; and Lena Struwe.
"Voucher Specimens are Essential for Documenting Source Material Used in Medicinal Plant Investigations."
Journal of Medicinally Active Plants