Study On Quantitative Analysis And Tempo-spatial Distribution Of 42 Species Of Dicksoniaceae From China

Dicksoniaceae is a basic group of Filicales and has important taxonomic position in ferns.And still their specific taxonomy is controversial.Quantitative analysis is a method which combines mathematical methods with statistical methods and botany.Because of its convenient and accurate,quantitative analysis has been applied to the classification of many plants in recent years.However,the quantitative analysis of the fossil Dicksoniaceae has not been reported yet.In addition,Dicksoniaceae is a ubiquitous element of the Jurassic to the Early Cretaceous periods and played an important role in the formation of flora.But the study on the temporal and spatial distribution and evolution of Dicksoniaceae is relatively fewer.In this paper,the data of 42 species of fossil Dicksoniaceae are analyzed by using cluster analysis,principal component analysis and correlation analysis.Combining with the morphological characters and distribution of extant related ferns,the classification,spatial and temporal distribution and evolution of Dicksoniaceae were studied,the conclusions are as follows:(1)Based on the quantitative analysis results of 42 species of Dicksoniaceae,28 species belonging to 4 genera were identified,and a key for their identification is given.(2)Based on the results of the quantitative analysis of 42 species,the discriminant models of 28 species were established,and were tested by the data of fossil Dicksoniaceae found in Yaojie Formation.The results show that the discriminant models have a certain accuracy and could apply in the identification of dicksoniaceae fossil plants in Yaojie Formation.(3)Based on the temporal and spatial distribution of fossil plants of Dicksoniaceae in China,found that the diversity of this Family has a northward reduced trend during Early Jurassic to Early Cretaceous.Accordingly this change could reflect that the warm-temperate humid climatic region,which is fit for Dicksoniaceae,has a similar changing trend.(4)The comparisons of morphological characteristics of Dicksoniaceae in different periods have been made,and found that Dicksoniaceae from Early Jurassic has smaller pinnules with relatively large sorus;Dicksoniaceae from Jurassic isrelatively thick,and pinnule is bigger,some have metamorphosis pinnules;Dicksoniaceae from Late Jurassic declined obviously,only a few survived to Early Cretaceous;Dicksoniaceae from Early Cretaceous are larger,and have intercalated pinnule.(5)Compared the morphological characters of Coniopteris with those of related extant genera in Cibotiaceae,Culcitaceae,Thyrsopteridaceae and Cyatheaceaethe,found that pinnae,pinnules,sori and indusia of Thyrsopteris are more similar to those of Coniopteris than to those of any other genus.And it is speculated that the morphological characteristics of indusium has an evolutionary ecological significance in the evolution of Dicksoniaceae.