Mirabilis himalaica (Edgew.) Heimerl (Nyctaginaceae) is endemic to the Himalayas where it is used in traditional Tibetan folk medicine and is the only Old World representative of a large New World genus. The systematic position of M. himalaica and historical biogeography of Mirabilis and related genera was evaluated using two loci (nuclear ribosomal internal transcribed spacer, rps16), with divergence times estimated using internal transcribed spacer sequences. All 16 sampled provenances of M. himalaica formed a strongly supported terminal clade and at the sectional level formed a clade with sect. Quamoclidion sensu stricto, despite their morphology. Section Oxybaphoides and sect. Oxybaphus were not closely related to M. himalaica, suggesting their apparent morphological similarities are convergent. The beast analysis and ancestral area reconstruction indicated that M. himalaica separated from related North American species during the late Miocene to early Pleistocene similar to 5.22 Ma (95% highest posterior density, 2.53-8.18). Both migration by way of the Quaternary Bering land bridge (Beringia) and long-distance dispersal could have contributed to the present-day disjunction between M. himalaica and the American species. These results agree with previous studies that suggest Oxybaphus should be merged into Mirabilis. However, although the infrageneric position of M. himalaica is still uncertain, it is not close to sect. Oxybaphus as has been suggested previously.