Fossil samaras of Ailanthus from South China and their phytogeographic implications

Ailanthus Desf. (Simaroubaceae), now widespread in southern Asia to northern Australia, was widely distributed in the Northern Hemisphere during the Cenozoic, but has few fossil records at low latitudes. Here we report the fossil samaras of Ailanthus confucii Unger from South China and its occurrences indicate that this genus has been distributed in low latitude regions since the middle Eocene. According to the recent fossil records, Ailanthus is considered to have originated from the Indian subcontinent and dispersed rapidly to East Asia and western North America following the early Paleogene onset of the India-Eurasia collision. In the Eocene, Ailanthus became widespread across the Northern Hemisphere. Subsequent to global cooling, Ailanthus gradually disappeared in the mid-high latitudes and may have continued to spread southward from Asia to northern Australia following the Asia-Australia collision in the late Oligocene, thus forming its modern distribution pattern.