Study On Ancestral Morphology Of Root And Stem Structure Of Chinese Ferns(Generalized)

Ferns are the earliest vascular plants with root,stem and leaf differentiation.Compared with the extensive research on seed plants and fern leaves,the research on fern roots and stems is lagging and scattered.So far,there has been no detailed and comprehensive discussion on whether they have ancestral characteristics.The classification of pteridophytes has always been widely concerned by scholars.There are obvious differences between the classical classification system represented by Qin Renchang system and the molecular classification system represented by PPG I system.This paper intends to comprehensively sample and observe the cross-sectional characteristics of the roots and stems of lycophytes and pteridophytes,analyze their consistency with Qin Renchang system and PPG I system,explore the ancestral characteristics of pteridophytes,and analyze the correlation between the cross-sectional characteristics of roots and stems and altitude,flora and habitat,so as to provide basic data for the study of the origin and evolution of pteridophytes.In this paper,74 species of lycophytes and pteridophytes in 32 families in China were studied.The cross-sectional characteristics of roots and stems of pteridophytes were observed and described by conventional paraffin section method.The cell diameter of each part of the cross-sectional surface was measured by Photoshop linear tool to analyze the cell uniformity,the proportion of each part of the cross-sectional surface was measured by equal area method to analyze the development degree,and the distribution type of cortical cells was studied by R software The correlation between sclerenchymal cell types and cortical cell wave patterns and altitude,flora and habitat is as follows:(1)This paper analyzes the differences between qinrenchang system and PPG I system,and summarizes four types of changes,including great changes in system status,simplification and merger of system classification,refinement and division of system classification,and changes in subordinate relationship of genus classification status.(2)The results showed that the probability of supporting PPG I system is 75%,and the probability of supporting qinrenchang system is 25%.(3)Eleven ancestral characteristics of pteridophytes were determined,including the uniformity of root cortical cells,the uniformity of vascular bundle cells,the development of cortex,the development of vascular bundle,the development of sclerenchyma,the development of parenchyma,the distribution type of cortical cells,cortical cell wave type,sclerenchyma cell type,the presence or absence of inclusions and vascular bundle sheath.These characteristics can be used as the basis for the classification of pteridophytes.(4)The classification system is properly adjusted by using the ancestral characteristics of the cross sections of roots and stems.The arrangement of families is mostly consistent with the PPG I system.The difference is that the cross section characteristics of the roots of Dryopteridaceae and Bolbitidaceae species are inconsistent in many aspects,such as the uniformity of cortical cells,the development of vascular bundles,the development of sclerenchyma tissue,the distribution type of cortical cells,the wave type of cortical cells,the type of sclerenchyma cells,the presence or absence of inclusions and the presence or absence of vascular bundle sheath,It is consistent only in the uniformity of vascular bundle cells and the development of cortex,and should not be combined with Dryopteridaceae;The cross-sectional characteristics of the roots of Polypodiaceae,Grammitidaceae and Loxogrammaceae are inconsistent in the uniformity of cortical cells,the uniformity of vascular bundle cells,the degree of cortical development,the degree of vascular bundle development,the wave pattern of cortical cells,the presence of inclusions and the presence of vascular bundle sheath.They are consistent only in the distribution type of cortical cells and the type of thick walled cells.Therefore,all families are separated and cannot be combined in Polypodiaceae.The adjustment of these two groups of differences extends the division method of Qin Renchang system.(5)The cortical cell distribution type,sclerenchyma cell type and cortical cell wave type of root are significantly correlated with altitude,flora and habitat,while the stem is basically irrelevant,which proves the important position and role of root in the evolutionary history of ferns,and provides some basic data for the study of plant physiology.(6)The initiation mode of stem xylem in lycophytes and pteridophytes is not a single internal initiation mode.The discovery of this phenomenon provides an anatomical basis for the study of "Root stem transition zone".At the same time,the characteristics of the cross section of the stem can not be used as the basis for tracing ancestors,which supports Nayer's root leaf origin theory,which provides basic data for the origin and evolution of pteridophytes.