Botanical DNA evidence in criminal cases: Knotgrass (Polygonum aviculare L.) as a model species

The possibilities and strategies for using DNA characteristics to link a botanical sample to a specific source plant or location vary with its breeding system. For inbreeding species, which often form small patches of identical genotypes, knotgrass (Polygonum aviculare L.) is a suitable model species because of its (1) occurrence in a wide range of natural environments, (2) abundant presence in pieces of evidence, and (3) ease in molecular processing. The value of knotgrass for forensic casework was demonstrated using data from a homicide case. Using the DNA fingerprinting technique AFLP(®) we were able to identify the knotgrass population at the crime site as the most likely origin of the botanical evidence. We expect that the development of tailored marker systems for knotgrass and other frequently occurring (model) species will considerably accelerate the use of botanical DNA evidence in criminal cases.