New fossil record of Cladium (Cyperaceae) from the Middle Miocene of Zhenyuan, SW China, and the palaeobiogeographical history of the genus

Monocotyledons first evolved in the early Cretaceous followed by marked diversification and range expansion in the Paleogene. However palaeobiogeographical studies of the Monocotyledons is rare. Here, we described the first fruit fossil record of Cladium zhenyuanensis X.Q. Liang & Z.K. Zhou (Cyperaceae) from the Middle Miocene of Zhenyuan, Yunnan, Southwest China. They are oblong or obovate with three distinct and longitudinal sulcate sutures with the base of the endocarps spread outwards in to three protrusions. Cells of the epicarp are rectangular with straight wall, mexocarps are thin and cell walls of endocarp are undulate. Discovery of these fossils indicated a wetland to the south of Ailao Shan in the Middle Miocene, and may have disappeared in the late Neogene because of rapid uplift of the Yungui Plateau. Based on fossil data, the first appearance of the genus was reported to be first appeared in Western Siberia in the Late Eocene, after which the genus migrated into Europe in the middle Oligocene and dispersed into Southeast Asia in the middle Miocene. The genus then expanded its distribution to North America and Africa in the Pliocene and Pleistocene by a long transoceanic dispersal.