Menodora is a genus of 23 species distributed in the temperate arid lands of North and South America and southern Africa. This distribution is similar to the pattern suggested by the boreotropical hypothesis, which implies an African origin, subsequent dispersal to North America via Europe over an Eocene land bridge during a global thermal maximum, and later dispersal to South America. This hypothesis was tested by reconstructing a phylogeny using data from sequences of the internal transcribed spacer (ITS) of nuclear ribosomal DNA, and the trnL intron, trnL-F spacer and rps16 intron of chloroplast DNA. In all parsimony analyses, most species formed monophyletic groups following continental lines. The single exception is the morphologically divergent Menodora spinescens of the Mojave Desert. It is consistently sister to a basal African clade in all trees in the rps16 intron analysis, and in most of the ITS and trnL/trnL-F trees. In the latter datasets, however, it appears in some trees as sister to the remaining New World species, and thus its position is uncertain. The remaining North American species are sister to the South American species in all analyses. Within the North American clade, several geographic patterns can also be noted. A group of Mexican species centered in the region around Galeana, Nuevo Leon forms a clade in all analyses, and a clade of central Mexican species is resolved in the ITS and trnL-F trees. Two species with overlapping distributions in Texas and Mexico, M. heterophylla and M. longiflora, are sister in both the ITS and rps16 trees. All data sets are highly congruent, and a combined analysis provides improved support overall but still does not resolve the position of M. spinescens at the base of the group. Nonetheless, the distribution of Menodora seems consistent with the pattern predicted by the boreotropic hypothesis.

Key words: biogeography, boreotropic hypothesis, ITS, Menodora, Oleaceae, rps16 intron, trnL intron, trnL-F spacer