The genus Lilaeopsis (Apiaceae subfamily Apioideae) comprises 15 species and exhibits both American amphitropic and amphiantarctic patterns of disjunction. The group is difficult taxonomically because of its simplified habit, phenotypic plasticity of vegetative characters, and extensive variation in fruit characters. Sequence data from the nrDNA ITS and cpDNA rps16 intron and rps16-trnK intergenic spacer regions were obtained for 60 accessions, representing 13 species of Lilaeopsis and five closely related outgroup genera from the North American Endemics clade of tribe Oenantheae. These molecular data were subjected to maximum parsimony, Bayesian inference, and dispersal-vicariance analyses in an effort to reconstruct evolutionary relationships and infer biogeographic scenarios. The results suggest that: (1) L. macloviana, L. masonii, and L. occidentalis, distributed in western South America and western North America, collectively represent a single, polymorphic species of amphitropic distribution; (2) The Australasian species L. brisbanica, L. novae-zelandiae, L. polyantha, and L. ruthiana comprise a well-supported clade. However, L. novae-zelandiae is not monophyletic, but may be rendered so by the inclusion of all Australasian taxa into one polymorphic species; (3) L. mauritiana from Mauritius is closely related to L. brasiliensis from South America and may even be subsumed under the latter pending further investigation; and (4) Lilaeopsis probably originated in South America following a dispersal of its ancestor from North America. A minimum of seven dispersal events is necessary to explain its present-day distribution, including one dispersal from South America to Australia or New Zealand, two dispersals between Australia and New Zealand, and three dispersals from South America to North America.