Intergeneric phylogenetic relationships within Apiaceae tribe Oenantheae were investigated using sequence data from the chloroplast DNA psbl-5'trnK((UUU)) and nuclear ribosomal DNA internal transcribed spacer regions. One hundred and thirty-one accessions were examined, representing all 17 genera of the tribe and approximately one-half of its species. The cpDNA region includes four intergenic spacers and the rps16 intron and these noncoding loci were analyzed separately to assess their relative utility for resolving relationships. Separate maximum parsimony analyses of the entire psbI-5'trnK((UUU))) and ITS regions, each with and without scored indels, yielded concordant trees. Phylogenies derived from maximum parsimony, Bayesian, or maximum likelihood analyses of combined chloroplast and nuclear DNA sequences for 82 accessions were highly resolved, well supported, and consistent. Among the five noncoding loci examined, the trnQ((UUG))-5'rps16 and 3'rps 16-5'trnK((UUU)) intergenic spacers are the most variable, with the latter contributing the greatest total number of parsimony informative characters relative to its size. The North American genera Atrema, Cynosciadium, Daucosma, Limnosciadium, Neogoezia, Oxgpolis, Ptilimnium, and Trepocarpus ally with the western hemispheric and Australasian genus Lilaeopsis in a strongly supported North American Endemics clade that is a sister group to a clade composed primarily of Old World taxa (Berula sensu lato, Cryptotaenia, Helosciadium, and Sium). Oxypolis and Ptilininium are not monophyletic, with the rachis-leaved members of each comprising a clade separate from their compound-leaved congeners. Dispersal-vicariance analysis suggests that the ancestors of the North American Endemics clade probably originated in Canada and the USA or in a broader ancestral area including Mexico and South America.
