Bidens pilosa L. is a plant producing barbed fruits which, due to its method of seed dispersal, is commonly found during forensic investigations. In Taiwan there are three varieties of the species, radiata, minor and pilosa. Fragments of these three varieties are difficult to differentiate by traditional morphological characteristics and until now little is known of their genetic composition. To discover genetic polymorphisms among these varieties, five loci within the nuclear and chloroplast genomes were screened. A total of 161 specimens were used in this study comprising different geographical populations. Seven samples of Bidens biternata were included as an out-group control. DNA fragments of all samples at the trnL intron and trnL-trnF IGS loci of the chloroplast genome, internal transcribed spacer (ITS1 and ITS2) and the 5.8S of nuclear ribosomal DNA (nrDNA) were amplified and sequenced. There were 3, 4, 20, 12 and 9 sequence types at these five loci, respectively. The sequence types for any locus of trnL intron, ITS1, ITS2 and 5.8S were found to be useful markers to identify Bidens biternata and B. pilosa. The resulting 84 haplotypes at the 5 loci could differentiate the var. radiata from the varieties of B. pilosa with only the exception of 1 type. The genetic polymorphisms can be used when comparing botanical remains to identify the variety of B. pilosa present at a crime scene.
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