Session 2B: Inaugural Lectures by Fellows / Associates

The Indian plate as a museum and evolutionary cradle for tropical angiosperms

Abstract: Tropical angiosperms are the main constituents of tropical biodiversity hotspots. Tracing the evolution of tropical angiosperms is arguably a challenging and relevant issue in plant evolution. The dramatic geological history of the Indian Plate puts on view its significant role in shaping the biogeography of tropical angiosperms. Dispersal routes between India and Madagascar till ~90-88Ma with Seychelles till 66Ma, with Africa through Kohistan Ladakh Arc (KLIA) during ~70-60Ma, and finally suturing with the Asian Plate ~50Ma onwards provides changing vegetation pattern on India plate as evident in the form of its fossil records. Early and Mid-Cretaceous sedimentary records of India have not provided any evidence of angiosperm fossils so far. Ecological opportunities due to latitudinal shift of the Indian plate in the tropical zone during Late Cretaceous-early Paleogene and the formation of dispersal routes with tropical Africa (via KLIA), and through that with Europe and later with Southeast Asia sheds light on the longstanding debate of lack of endemicity of Indian fossil flora despite isolation of Indian plate as an island. KLIA acted as a filter corridor for dispersal of tropical angiosperms from Africa to India. Perhumid climatic setting due to equatorial positioning of Indian Plate under warm climate of early Paleogene provided an ecological release for the rapid diversification and speciation of aseasonal tropical angiosperms. Post-India Asia collision led to the dispersal of the aseasonal tropical angiosperms to the low-lying tropical regions of Southeast Asia where they got an ecological release afresh, helping them speciate again and diversify to finally develop as dense tropical rain forests. These warm and humid climatic conditions were maintained for the sustainability of tropical angiosperms on Indian plate till the initiation of monsoonal climate. Lesser precipitation and long periods of dry climatic conditions with the advent of monsoonal climate led to the retraction of aseasonal tropical angiosperms from larger parts of India and restricted them to the perhumid climate of the Southwestern Ghats of India and Sri Lanka as Gondwana relic forests. The Indian Plate hence acted as both museum and cradle for tropical biodiversity and was the main driver for the emergence of tropical rain forest in Southeast Asia