Late Pliocene Smilax (Smilacaceae) leaves from Southwest China: Phytogeographical and paleoecological implications

Abundant fossil records indicate that the genus Smilax L. was widely distributed in North America and Europe during the Paleogene and thrived in the Miocene. However, since the early Pliocene, the fossil occurrence of Smilax has become very rare. In this study, we describe three leaf taxa of Smilax from the upper Pliocene of West Yunnan, Southwest China based on their leaf architecture and cuticle features. Smilax tengchongensis sp. nov. and Smilax cf. bracteata Presl differ from each other both in leaf shape and cuticle features. The leaves of Smilax sp. possess a different shape and venation but share similar cuticle features with those of S. tengchongensis sp. nov. The morphological diversity of our fossils indicates that a warm and humid climate with a multilayered structure existed in the Pliocene forests of West Yunnan. Moreover, recent molecular studies indicate that both New World and Old World species of Smilax exhibited an intercontinental disjunct distribution via the Beringia land bridge between East Asia and North America. However, this biogeographic disjunction is not well demonstrated by the fossil records as a result of inadequate paleobotanical data.