Evolution of family Arecaceae on the Indian Plate modulated by the Early Palaeogene climate and tectonics

Arecaceae (palms) is a pantropical plant family with an ancient origin. It shows distinct spatial patterns of species richness in tropical regions having greatest diversity within the Neotropical regions and Southeast Asia. The wider palaeobiogeographic records of palms in relation to current distribution requires a re-examination of their palaeobiogeographic history. The present study reports eleven fossil pollen form-species from the early Palaeogene of India, enhancing our understanding of the evolution of four palm subfamilies: Arecoideae, Calamoideae, Coryphoideae and Nypoideae, on the Indian Plate prior to the India-Asia collision. We suggest the dispersal of diverse palms from Africa to India via the Kohistan- Ladakh Island Arc during Maastrichtian-Palaeocene as part of the Africa-India Floristic Interchange. Subsequently, with wet and humid climates across much of the Indian Plate during the Palaeocene-early Eocene, they underwent a phase of diversification and adaptation leading to habitat expansion. Thus, Indian Plate served as an evolutionary hotspot for the diversification of palms during the early Palaeogene. An in-depth investigation of Palaeogene palm fossils revealed that many palms, currently endemic to Southeast Asia, initially evolved and diversified on the Indian Plate and later dispersed to Southeast Asia following India-Asia collision. The present study thus favours the "Out-of-India" dispersal hypothesis for the Asian palms. The expansion of seasonal climates, and aridification during Neogene and Quaternary led extinction in numerous palm lineages on the Indian subcontinent. This study proposes that deep time climate change and plate tectonism have highly influenced the heterogeneity in spatial and temporal distribution of Asian palms.