Fossil leaves of Populus from the Middle Miocene of Yunnan, SW China

Today southern Yunnan, SW China, has a tropical or subtropical climate and seasonal rainforests. In the past, some temperate elements were also present. In this paper, a new species of n Populus n is reported from the Middle Miocene deposits in Zhenyuan. Its leaves are ovate or ovate-suborbicular, with serrate margins. They have a shallowly cordate to cuneate base without glands, short acuminate apex, and salicoid teeth with spherical glands. The veins are glabrous but unicellular hair bases occur on the lower epidermis of the lamina. Stomata are confined to the lower epidermis. The presence of n Populus n in the Middle Miocene of the region indicates an expansion of the genus into low-latitude Asia in the late Cenozoic and a more complicated history of vegetational change in southern Yunnan than has so far been assumed.