Anatomical Structure And Geological Significance Of Reproductive Organs Of Several Gymnosperms From The Lower Cretaceous Of Mazongshan,gansu Province

The gymnosperms are an important part of modern forest vegetation,and they are also the main types of Mesozoic flora.The morphological structures of the gymnosperms reproductive organs are relatively stable,which is important for the classification and identification,and exploration the origin and evolution of gymnosperms plants.The Cretaceous is represented by the Greenhouse Climate.Study of Cretaceous plants is of great significance to understand the ecological environment under the Greenhouse Climate.The Lower Cretaceous of Mazongshan is widely distributed and well exposed,and rich in plant fossils,while the related researches are relatively poor.In recent years,many gymnosperm reproductive organ fossils,including Cycads,Ginkgo and Conifer were collected from the Lower Cretaceous of Mazongshan,western Gansu Province,and the fossils are studied both morphologically and anatomically.A total of 8 species of 4 genera are reported and described.Including a new species of Cycads,Phasmatocycas mazongshanensis sp.nov.;2 genera and 3 species of Ginkgo,such as Leptostrobus sphaericus,Stenorachis opulent sp.nov.and Stenorachis bellus;3 genera and 4 species of Conifers,including Elatides harrisii,Carpolithus mazongshanensis,Carpolithus cf.jidongensis and Pityostrobus sp.All the species are studied by using the Optical Microscope,Fluorescence Microscope and Scanning Electron Microscope.In addition,according to the macro-morphological and micromorphological characteristics,the affinity of several taxons was discussed.It is believed that Leptostrobus should be classified as the Czekanowskiales;Stenorachis is the reproductive organ of the Ginkgoales;Elatides and Cunninghamia are closely related;Carpolithus cf.jidongensis and Carpolithus mazongshanensis may related to the Cupressaceae,and particularly Platycladus.Finally,Stenorachis has long petiole and numerous ovules.The systematic evolution analysis showed that Stenorachis is quite different from the Ginkgo biloba and is closer to the primitive type.In addition,Stenorachis may be in the same evolutionary series as Trichopitys and Schmeissneria.Moreover,the combination analysis of the Elatides records and paleoclimate and paleoenvironment conditions from the Early Jurassic to Early Cretaceous of China showed that Elatides is sensitive to environment and climate change,and its distribution migrated with the migration of the climatic zones.