Given are some statements with reference to the use of genes in plant molecular systematics.

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Chloroplast DNA (cpDNA) is a traditional workhorse for reconstructing evolutionary relationships among angiosperms. The frequent use of cpDNA in such analyses is predicated on the apparent simplicity of its inheritance: uniparental through the maternal line, and lacking biparental recombination. Hence Statement B is wrong. Since the cpDNA molecule is highly conserved, there is very little intra-specific variation, and cpDNA-based RFLP studies have therefore mostly been conducted on an inter-specific level. By contrast, plant mitochondria have never been much used in molecular analyses. The major reason is that while the plant mitochondrial DNA (mtDNA) sequence is usually highly conserved, the size and structure of mtDNA molecules may vary widely even within individual plants. Moreover, recent studies indicated that substitution rates of mtDNA genes can vary enormously even among closely related plant species. Hence statement A is correct. The 16S–23S internally transcribed spacer (ITS) regions of the rRNA operon might be under minimal selective pressure during evolution and therefore have more variation in the sequences than that of the coding regions of 16S and 23S rRNAs. While the sequence of the rRNA genes evolves slowly, the internal transcribed spacers (ITS1 and ITS2), the external transcribed spacer (ETS), and the intergenic spacer (IGS) evolve rapidly. Hence statement C is correct.