Duabanga (Lythraceae) from the Oligocene of India and its climatic and phytogeographic significance

Understanding the evolutionary history of biodiversity hotspots has important implications for their future survival. India hosts four biodiversity hotspots: the Western Ghats of South India, the Andaman and Nicobar Islands, the Eastern Himalaya, and the Indo-Myanmar region. Northeast India (NEI) is an important region that hosts 43% of the total plant species occurring in India, of which ∼39% are endemic. This region also acts as a gateway for biotic exchange between India and southeast Asia. The area also receives exceptional rainfall during the pre-monsoon (March to May), in addition to the summer monsoon (June to September) season. In rainforests of NEI, forest-forming plant species make up a large proportion of the biodiversity. Understanding the evolutionary history of rainforests of NEI has implications for the conservation of biodiversity hotspots. Here we report the evergreen rainforest genus Duabanga Buch.-Ham. of the family Lythraceae from the late Oligocene sediments of Assam, NEI. Fossil records of this genus (from south and southeast Asia) suggest its Gondwanan origin, while its modern distribution is dominantly controlled by moisture availability.