Biogeographical diversification of mainland Asian Dendrobium (Orchidaceae) and its implications for the historical dynamics of evergreen broad-leaved forests.

Aim: Evergreen broad-leaved forests (EBLFs) occupy most tropical and subtropical regions of mainland Asia and exhibit high species diversity, productivity and richness. Understanding the historical dynamics of EBLFs is important for biodiversity conservation and regional carbon storage and cycling under global climate change. However, little is known about the historical dynamics of EBLFs in mainland Asia. Dendrobium, an epiphytic orchid genus found in EBLFs, was used to gain new insights of the historical establishment and extension of EBLFs in mainland Asia. Location: Mainland Asia. Methods: We sampled c. 80% of the currently recognized species of Dendrobium found in mainland Asia. A phylogeny was generated using maximum parsimony, maximum likelihood and Bayesian inference methods. A calibrated chronogram was obtained using a Bayesian relaxed-clock model approach. Biogeographical scenarios were investigated using the statistical dispersal- vicariance analysis and dispersal-extinction-cladogenesis methods. Ancestral states were constructed by mesquite and bayestraits, and diversification of Dendrobium was investigated by APE and LASER packages. Results Our results indicate that Asian Dendrobium was present on mainland Asia since the Oligocene, after which this genus diversified in this region and dispersed into higher elevations. The ancestral habit of Dendrobium was epiphytic and terrestrial and lithophytic habits each have multiple, recently independent origins. Main conclusions Our results support the hypothesis that EBLFs have been established in mainland Asia at least since the Oligocene and further suggest that the EBLFs of mainland Asia expanded into higher elevations prior to the late Cenozoic. The diversification of Asian Dendrobium coincided with a warmer climate during the late Oligocene and middle Miocene and the expansion of key groups (including Fagaceae, Lauraceae, Magnoliaceae and Theaceae) of EBLFs during the early Cenozoic. [ABSTRACT FROM AUTHOR]