Every sample that is derived from another specimen/sample is a child of that specimen/sample. The original individual in the field is not cataloged, so it is not a parent. The bottommost DNA extract is a child of the bottommost tissue sample, which is a child of the voucher specimen.  
  Part of: Funk V, Gostel M, Devine A, Kelloff C, Wurdack K, Tuccinardi C, Radosavljevic A, Peters M, Coddington J (2017) Guidelines for collecting vouchers and tissues intended for genomic work (Smithsonian Institution): Botany Best Practices. Biodiversity Data Journal 5: e11625. https://doi.org/10.3897/BDJ.5.e11625