The slipper orchids are widely distributed in temperate to tropical regions of Eurasia and America. The genus Cypripedium occurs in temperate and subtropical areas of the North Hemisphere, with some species extending to tropical North America. The two conduplicate-leaved genera Mexipedium and Phragmipedium and the plicate-leaved genus Selenipedium are restricted to the neotropics, whereas Paphiopedilum is confined to the palaeotropics (Fig. 1). Atwood [62] and Albert [63] supported the boreotropical hypothesis [66], and considered that fragmentation of continents and the following climatic cooling in the Ice Ages caused the present disjunct distribution of slipper orchids. While the ITS analysis supports southern North America/Mesoamerica as the origin center of slipper orchids [64], the sister relationship between Mexipedium and Paphiopedilum revealed in the low copy nuclear Xdh gene phylogeny [48], although with weak support and based on a limited sampling, seems to suggest a long distance dispersal from palaeotropical to neotropical regions. Therefore, the biogeographical history of slipper orchids is far from being resolved.