The Western Ghats is a biodiversity hotspot extending along the west coast
of India. It has a high endemism and harbours over 5000 plant species.
Whereas, the evergreen forests populating the wet zone on the western
slopes have existed since 65 million years ago, the deciduous forests
populating the eastern plateau were established during the Miocene
aridification about 10 million years ago. Additionally, the wet zone also
has a latitudinal gradient in length of dry period that was established
after the intensification of the monsoons and thus affects species
composition, with the relict evergreen species largely confined to the
southern refuge pocket. In this study, we tested the antiquity of the
evergreen forests, the southern refuge hypothesis, and the relationship of
species across these forest types.

We found evergreen forests show antiquity compared to deciduous forests,
and PD patterns corroborates the southern refuge hypothesis. Most
interestingly, deciduous forest species show shared evolutionary histories
with evergreen forest species, suggesting shifts in this trait, whereas
evergreen forests show greater disparate histories possibly due to their
antiquity and sharper gradients in the wet zone.