Tertiary leaf fossils of Mangifera (Anacardiaceae) from Li Basin, Thailand as examples of the utility of leaf marginal venation characters

摘要

The mango (Mangifera) is the most important commercial fruit in Asia and is popular worldwide. Because of uncertainty in its origin and biogeography, the study of Mangifera could be of value in elucidating its current genetic diversity and geographical distribution. We report here two new species of compressed leaves of Mangifera (Anacardiaceae) from upper Oligocene-lower Miocene lacustrine sediments in the Li Basin, northern Thailand. Leaf form and venation characters of fossil and extant leaves are presented with detailed marginal venation patterns that were found to be important in assigning the fossil leaves to Mangifera paleoindica and M. paleocaloneura. These two fossil species of Mangifera and the present occurrence of basal species of Mangifera in Thailand suggest that northern Thailand could be an area with a long history of evolution and diversification of Mangifera, particularly M. indica.