Abstract: The Asian paleotropical flora is characterized by abundance of endemic species, high biodiversity, and complex geological and climatic histories. However, the main driving mechanism underlying such high tropical biodiversity remains unclear. Hence, the present study aims to investigate the biogeographic origin of the Asian paleotropical flora by tracking the speciation and diversification history of a typical tropical perennial, Typhonium s.s. (Araceae), using a time-calibrated whole-plastome phylogeny. In particular, we tested whether the Asian paleotropic region is a macroevolutionary source or sink. We observed that Typhonium s.s. originated in Indochina during the early-middle Miocene, approximately 17.24 Ma [95% highest posterior density (HPD): 12.83 ̶ 21.99 Ma]. Most of the in situ diversification within the genus Typhonium s.s. have been underway since 14.73 Ma, with an accelerated lineage diversification at ca. 15-17 Ma, which may have been triggered by the intensification of the Asian monsoon system around the middle Miocene. Furthermore, the underground tuberous stem of Typhonium s.s. might have played an essential role in the adaptation to the seasonality caused by the monsoon in Indochina. Our results also suggested that peripatric speciation may be important in the diversification of T. trilobatum and T. roxburghii. This study provides a framework for studies in biogeography and evolution of the Asian paleotropical flora.

Key words: Asian monsoon, biodiversity hotspots, floristic region, Old World Tropic, peripatric speciation