The Study On The Ancestral Morphology Of Petioles(Rachis) Structure Of True Ferns In China

True ferns are the main group of modern ferns,and their classification is controversial.In the past,due to the limitations of scientific and technological means,the morphological classification system represented by the Qin Renchang system has been used.In recent years,the molecular classification system represented by the PPG I system has gradually been widely accepted.But,due to the lack of strong evidence of morphological ancestry in molecular classification systems,the conclusions drawn are still controversial.And in order to fully understand the problems related to the systematic classification of ferns,it is necessary to deeply and carefully study the anatomical characteristics.When there is a large contradiction between the modern molecular classification system and the classical morphological classification system,it can still be classified by systematically comparing anatomical features.Because true ferns have developed leaves,and the cross-section characteristics of petiole or rachis are richer than those of longitudinal section,this paper systematically observed the cross-section characteristics of petioles(rachis)of 80 species of 32 families of Chinese true ferns in PPG I system for the first time.We compared and analyzed the transverse cutting characteristics from the tissue level,calculated the proportion of each tissue and the cell diameter method to calculate the cell uniformity by the isometric area method;for the first time,the distribution type of petiole(rachis)cortex cells and the thickening method of cells outside the vascular bundle were summarized;the classical morphological classification system and molecular classification system,namely Qin Renchang system and PPG I system,were selected,and the two classification systems were evaluated from the perspective of anatomy,and the ancestral characteristics were found;on this basis,the correlation between classification systems and the ancestral characteristics,and the correlation between some cross-cutting features and single factor of altitude,flora and habitat were analyzed.A large number of morphological comparison work is done to improve the information on the transverse characteristics of petioles(rachis)in morphological classification,provide morphological evidence for molecular classification systems,help clarify interfariage relationships,and provide basic materials for the systematic understanding of petioles(rachis)of true ferns.The results of this paper are as follows:(1)The distribution types of thick-walled tissue are divided into 7 types,namely P type,S type,S-P type,S-P-S type,P-S type,P-S-P type and P-S-P-S type.(2)There are four types of thick-walled cells outside the vascular bundle,namely,single-sided,double-sided,three-sided,and four-sided thickening.(3)Hymenophyllaceae,Dipteridaceae,Plagiogyriaceae,Dennstaedtiaceae,Athyriaceae,Blechnaceae,Hypodematiaceae,Aspidiaceae,Polypodiaceae support PPG I system,and Lindsaeaceae supports Qin Renchang system.(4)There are 14 ancestral features,including the proportion of epidermis,the number of subepidermal sclerenchymal cells,the proportion of cortex,the uniformity of sclerenchymal cells,the uniformity of parenchymal cells,the distribution type of cortical cells,the number of sclerenchymal cells outside the vascular bundle,the thickening method of sclerenchymal cells outside the vascular bundle,the shape of cortical cells,the tightness of cortical cells,whether there are inclusions,the proportion of vascular bundles and the uniformity of vascular bundle cells.These ancestral features have a certain stability in the family and have a certain significance for the division of the family.(5)Qin Renchang system and PPG ? system are related to ancestral features,and the correlation is strong,so the ancestral features in this paper can provide a certain theoretical basis for the morphological classification,and provide morphological evidence for the molecular classification system.(6)The correlation analysis of the five cross-section features with altitude,flora and habitat showed that: the distribution type of cortical cells,the shape of cortical cells,the proportion of cortex,thickening of vascular bundles of thick-walled cells were not related to altitude,flora and habitat,and the tightness of cortical cells was related to altitude and flora,and was not related to habitat.Among them,cortical cell density is not only an ancestral feature,but also related to altitude and flora.This result can provide ideas for studying the relationship between genetic structure and environmental heterogeneity,morphological variation and so on.