A molecular systematic investigation of Cymopterus and its allies (Apiaceae) based on phylogenetic analyses of nuclear (ITS) and plastid (rps16 intron) DNA sequences

Considerable controversy exists with regard to the proper delimitation of Cymopterus (Apiaceae subfamily Apioideae) and its relationship to the other perennial endemic umbellifers of western North America. Previous molecular systematic studies using nuclear (rDNA ITS) and, for subsets of taxa, plastid (rps16 intron and trnF-trnL-trnT) DNA sequences have revealed that the genus Cymopterus is polyphyletic, with its species inextricably linked with those of Aletes, Lomatium, Musineon, Oreoxis, Pseudocymopterus, Pteryxia, Tauschia, and several other genera of the region. Herein, in an effort to increase resolution of relationships, we procured rps16 intron sequence data from 74 accessions of Cymopterus and its allies so that ITS and intron matrices are available for the same set of 129 taxa. These data matrices were analysed, separately and in combination, using maximum parsimony and (or) maximum likelihood methods. For those trees exhibiting the greatest resolution, the results revealed that the perennial, endemic apioid genera of North America (north of Mexico) comprise a weakly supported monophyletic group, with Angelica constituting its sister lineage. Cymopterus is confirmed as highly polyphyletic. The rps16 intron yielded substantially fewer parsimony informative characters than those of the ITS region and when analysed, separately or in combination, with ITS data, resulted in trees of poor resolution. Only one previously identified species group of Cymopterus is supported as monophyletic; this group coincides with section Phellopterus, and is recognised by its showy, basally connate bractlets. Many other genera endemic to western North America appear to be highly artificial assemblages of species that will likely be abandoned in any revised system of umbellifer classification.