Molecular systematics of Apiaceae subfamily Apioideae: phylogenetic analyses of nuclear ribosomal DNA internal transcribed spacer and plastid RPO C1 intron sequences

Evolutionary relationships among representatives of Apiaceae (Umbelliferae) subfamily Apioideae have been inferred from phylogenetic analyses of nuclear ribosomal DNA internal transcribed spacer (ITS 1 and ITS 2) and plastid rpoC1 intron sequences. High levels of nucleotide sequence variation preclude the use of the ITS region for examining relationships across subfamilial boundaries in Apiaceae, whereas the rpoC1 intron is more suitably conserved for family-wide phylogenetic study but is too conserved for examining relationships among closely related taxa. In total, 126 ITS sequences from subfamily Apioideae and 100 rpoC1 intron sequences from Apiaceae (all three subfamilies) and outgroups Araliaceae and Pittosporaceae were examined. Phylogenies estimated using parsimony, neighbor-joining, and maximum likelihood methods reveal that: (1) Apiaceae subfamily Apioideae is monophyletic and is sister group to Apiaceae subfamily Saniculoideae; (2) Apiaceae subfamily Hydrocotyloideae is not monophyletic, with some members strongly allied to Araliaceae and others to Apioideae + Saniculoideae; and (3) Apiaceae subfamily Apioideae comprises several well-supported subclades, but none of these coincide with previously recognized tribal divisions based largely on morphological and anatomical characters of the fruit. Four major clades in Apioideae are provisionally recognized and provide the framework for future lower level phylogenetic analyses. A putative secondary structure model of the Daucus carota (carrot) rpoC1 group II intron is presented. Of its six major structural domains, domains II and III are the most, and domains V and VI the least, variable.