Pedaliaceae and Martyniaceae are Old World and New World families occurring primarily in arid environments with some taxa exhibiting similar adaptations to dispersal by large animals. Their taxonomic histories have also been intertwined, since they have often been combined as one family (e.g. Pedaliaceae). The temperate Asian aquatic plant Trapella was also assigned to Pedaliaceae, based on fruits with similar dispersal traits. With expanded sampling of both families, including Trapella, and data from ndhF, trnLF, and ETS sequences, this study confirms that the two families are distinct lineages, identifies a new placement for Trapella in tribe Gratioleae (Plantaginaceae s. 1), and shows that the two families exhibit a combination of shared floral morphology due to their proximity in Lamiales, and convergent functional morphology for dispersal. The phylogeny indicates the three tribes of Pedaliaceae are monophyletic, but that Sesamum is not.