Ailanthus (Simaroubaceae) is easily recognized in the fossil record based on winged fruits (samaroid mericarps with a centrally placed seed) and is well represented in the Tertiary of North America, Asia, and Europe. The fruits are typically found in lacustrine shales as impressions with a distinctive elliptical shape, reticulate venation covering the seed, and elongated reticulate venation running the length of the wing. The earliest occurrences are in the Early Eocene of North America and Asia, and the Middle Eocene of Europe. The youngest fossil occurrences are from the Middle Miocene of North America, the Pliocene of Europe, and the Pleistocene of Asia. The genus occurs native today from southeast Asia to Australia. No fossils have yet been discovered from eastern North America or from the area of modern distribution. This assessment of the Ailanthus fossil record is based on fruits observed in paleobotanical collections and those illustrated with convincing photographs in the literature. Nomenclature of the fossil fruits is problematic due to lack of distinguishing characters among North American (A. americana Cockerell), European (A. confucii Unger), and Asian (A. youngi Hu and Chaney) specimens. The fossil specimens are similar to the modern species A. altissima (Mill.) Swingle; however, they differ from the larger modern A. triphysa (Dennst.) Alston and A. integrifolia Lam. The stratigraphic and geographic records of Ailanthus fossil fruits indicate a possible western North American or eastern Asian origin of the genus. Absence from Cretaceous and Paleocene sites suggests an Eocene origin of the genus. Ailanthus is positioned basally within the Simaroubaceae according to chemical and molecular evidence of previous authors. The fossil history of Ailanthus establishes a minimum age of Early Eocene for the Simaroubaceae. This conclusion is consistent with Miocene occurrences of Leitneria, the only other genus of the family with a reliable fossil record.

Key words: Ailanthus, biogeography, fossil fruits, phytogeography, Simaroubaceae