title: First occurrence of Platycladus from the upper Miocene of Southwest China and its phytogeographic implications.
abstract: Platycladus Spach is native to Central China, but its natural occurrences are very difficult to establish. According to molecular phylogenetic data, this genus might have originated since the Oligocene, but no fossil record has been reported. Here, we describe eight foliage branches from the upper Miocene in western Yunnan, Southwest China as a new species, P. yunnanensis sp. nov., which is characterized by foliage branches spread in flattened sprays, and leaves decussate, imbricate, scale-like and dimorphic. The leaves are amphistomatic, and the stomata are elliptical or oblong, haplocheilic, and monocyclic type. Based on a detailed comparison with the extant genera of Cupressaceae sensu lato, our fossils are classified into the genus Platycladus. The occurrence of P. yunnanensis sp. nov. indicates that this genus had a more southernly natural distribution in the late Miocene than at present. Molecular phylogeny and fossil records support a pre-Oligocene common ancestor for the genera Platycladus, Microbiota and Calocedrus. The separation of the three taxa was most likely caused by the arid belt across Central China during the Oligocene. In addition, the cooling down of the global temperature and the strengthening of Asian monsoon since the Miocene will further promote the migration of these genera.
authors.affiliation: Key Laboratory of Mineral Resources in Western China (Gansu Province), School of Earth Sciences, and College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China; State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, CAS, Nanjing, 210008, China.
authors.forename: Jing-Yu
authors.initials: JY
authors.lastname: Wu
authors.affiliation: Key Laboratory of Mineral Resources in Western China (Gansu Province), School of Earth Sciences, and College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Su-Ting
authors.initials: ST
authors.lastname: Ding
authors.affiliation: Key Laboratory of Mineral Resources in Western China (Gansu Province), School of Earth Sciences, and College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Qi-Jia
authors.initials: QJ
authors.lastname: Li
authors.affiliation: Key Laboratory of Mineral Resources in Western China (Gansu Province), School of Earth Sciences, and College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Zhen-Rui
authors.initials: ZR
authors.lastname: Zhao
authors.affiliation: Key Laboratory of Mineral Resources in Western China (Gansu Province), School of Earth Sciences, and College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Bai-Nian
authors.initials: BN
authors.lastname: Sun
mesh_terms: D005075:Biological Evolution; D002681:China; D029779:Cupressaceae / Q000033:anatomy & histology / Q000145:classification* / Q000254:growth & development; D005580:Fossils; D005843:Geography; D010802:Phylogeny; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000254:growth & development